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  1. <?xml version="1.0" encoding="UTF-8" standalone="no"?>

  2. <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><title>42.6. Control Structures</title><link rel="stylesheet" type="text/css" href="stylesheet.css" /><link rev="made" href="pgsql-docs@lists.postgresql.org" /><meta name="generator" content="DocBook XSL Stylesheets V1.79.1" /><link rel="prev" href="plpgsql-statements.html" title="42.5. Basic Statements" /><link rel="next" href="plpgsql-cursors.html" title="42.7. Cursors" /></head><body><div xmlns="http://www.w3.org/TR/xhtml1/transitional" class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="5" align="center">42.6. Control Structures</th></tr><tr><td width="10%" align="left"><a accesskey="p" href="plpgsql-statements.html" title="42.5. Basic Statements">Prev</a> </td><td width="10%" align="left"><a accesskey="u" href="plpgsql.html" title="Chapter 42. PL/pgSQL - SQL Procedural Language">Up</a></td><th width="60%" align="center">Chapter 42. <span xmlns="http://www.w3.org/1999/xhtml" class="application">PL/pgSQL</span> - <acronym xmlns="http://www.w3.org/1999/xhtml" class="acronym">SQL</acronym> Procedural Language</th><td width="10%" align="right"><a accesskey="h" href="index.html" title="PostgreSQL 12.4 Documentation">Home</a></td><td width="10%" align="right"> <a accesskey="n" href="plpgsql-cursors.html" title="42.7. Cursors">Next</a></td></tr></table><hr></hr></div><div class="sect1" id="PLPGSQL-CONTROL-STRUCTURES"><div class="titlepage"><div><div><h2 class="title" style="clear: both">42.6. Control Structures</h2></div></div></div><div class="toc"><dl class="toc"><dt><span class="sect2"><a href="plpgsql-control-structures.html#PLPGSQL-STATEMENTS-RETURNING">42.6.1. Returning From a Function</a></span></dt><dt><span class="sect2"><a href="plpgsql-control-structures.html#PLPGSQL-STATEMENTS-RETURNING-PROCEDURE">42.6.2. Returning from a Procedure</a></span></dt><dt><span class="sect2"><a href="plpgsql-control-structures.html#PLPGSQL-STATEMENTS-CALLING-PROCEDURE">42.6.3. Calling a Procedure</a></span></dt><dt><span class="sect2"><a href="plpgsql-control-structures.html#PLPGSQL-CONDITIONALS">42.6.4. Conditionals</a></span></dt><dt><span class="sect2"><a href="plpgsql-control-structures.html#PLPGSQL-CONTROL-STRUCTURES-LOOPS">42.6.5. Simple Loops</a></span></dt><dt><span class="sect2"><a href="plpgsql-control-structures.html#PLPGSQL-RECORDS-ITERATING">42.6.6. Looping through Query Results</a></span></dt><dt><span class="sect2"><a href="plpgsql-control-structures.html#PLPGSQL-FOREACH-ARRAY">42.6.7. Looping through Arrays</a></span></dt><dt><span class="sect2"><a href="plpgsql-control-structures.html#PLPGSQL-ERROR-TRAPPING">42.6.8. Trapping Errors</a></span></dt><dt><span class="sect2"><a href="plpgsql-control-structures.html#PLPGSQL-CALL-STACK">42.6.9. Obtaining Execution Location Information</a></span></dt></dl></div><p>

  3.     Control structures are probably the most useful (and

  4.     important) part of <span class="application">PL/pgSQL</span>. With

  5.     <span class="application">PL/pgSQL</span>'s control structures,

  6.     you can manipulate <span class="productname">PostgreSQL</span> data in a very

  7.     flexible and powerful way.

  8.    </p><div class="sect2" id="PLPGSQL-STATEMENTS-RETURNING"><div class="titlepage"><div><div><h3 class="title">42.6.1. Returning From a Function</h3></div></div></div><p>

  9.      There are two commands available that allow you to return data

  10.      from a function: <code class="command">RETURN</code> and <code class="command">RETURN

  11.      NEXT</code>.

  12.     </p><div class="sect3" id="id-1.8.8.8.3.3"><div class="titlepage"><div><div><h4 class="title">42.6.1.1. <code class="command">RETURN</code></h4></div></div></div><pre class="synopsis">

  13. RETURN <em class="replaceable"><code>expression</code></em>;

  14. </pre><p>

  15.       <code class="command">RETURN</code> with an expression terminates the

  16.       function and returns the value of

  17.       <em class="replaceable"><code>expression</code></em> to the caller.  This form

  18.       is used for <span class="application">PL/pgSQL</span> functions that do

  19.       not return a set.

  20.      </p><p>

  21.       In a function that returns a scalar type, the expression's result will

  22.       automatically be cast into the function's return type as described for

  23.       assignments.  But to return a composite (row) value, you must write an

  24.       expression delivering exactly the requested column set.  This may

  25.       require use of explicit casting.

  26.      </p><p>

  27.       If you declared the function with output parameters, write just

  28.       <code class="command">RETURN</code> with no expression.  The current values

  29.       of the output parameter variables will be returned.

  30.      </p><p>

  31.       If you declared the function to return <code class="type">void</code>, a

  32.       <code class="command">RETURN</code> statement can be used to exit the function

  33.       early; but do not write an expression following

  34.       <code class="command">RETURN</code>.

  35.      </p><p>

  36.       The return value of a function cannot be left undefined. If

  37.       control reaches the end of the top-level block of the function

  38.       without hitting a <code class="command">RETURN</code> statement, a run-time

  39.       error will occur.  This restriction does not apply to functions

  40.       with output parameters and functions returning <code class="type">void</code>,

  41.       however.  In those cases a <code class="command">RETURN</code> statement is

  42.       automatically executed if the top-level block finishes.

  43.      </p><p>

  44.       Some examples:

  45. 

  46. </p><pre class="programlisting">

  47. -- functions returning a scalar type

  48. RETURN 1 + 2;

  49. RETURN scalar_var;

  50. 

  51. -- functions returning a composite type

  52. RETURN composite_type_var;

  53. RETURN (1, 2, 'three'::text);  -- must cast columns to correct types

  54. </pre><p>

  55.      </p></div><div class="sect3" id="id-1.8.8.8.3.4"><div class="titlepage"><div><div><h4 class="title">42.6.1.2. <code class="command">RETURN NEXT</code> and <code class="command">RETURN QUERY</code></h4></div></div></div><a id="id-1.8.8.8.3.4.2" class="indexterm"></a><a id="id-1.8.8.8.3.4.3" class="indexterm"></a><pre class="synopsis">

  56. RETURN NEXT <em class="replaceable"><code>expression</code></em>;

  57. RETURN QUERY <em class="replaceable"><code>query</code></em>;

  58. RETURN QUERY EXECUTE <em class="replaceable"><code>command-string</code></em> [<span class="optional"> USING <em class="replaceable"><code>expression</code></em> [<span class="optional">, ... </span>] </span>];

  59. </pre><p>

  60.       When a <span class="application">PL/pgSQL</span> function is declared to return

  61.       <code class="literal">SETOF <em class="replaceable"><code>sometype</code></em></code>, the procedure

  62.       to follow is slightly different.  In that case, the individual

  63.       items to return are specified by a sequence of <code class="command">RETURN

  64.       NEXT</code> or <code class="command">RETURN QUERY</code> commands, and

  65.       then a final <code class="command">RETURN</code> command with no argument

  66.       is used to indicate that the function has finished executing.

  67.       <code class="command">RETURN NEXT</code> can be used with both scalar and

  68.       composite data types; with a composite result type, an entire

  69.       <span class="quote">“<span class="quote">table</span>”</span> of results will be returned.

  70.       <code class="command">RETURN QUERY</code> appends the results of executing

  71.       a query to the function's result set. <code class="command">RETURN

  72.       NEXT</code> and <code class="command">RETURN QUERY</code> can be freely

  73.       intermixed in a single set-returning function, in which case

  74.       their results will be concatenated.

  75.      </p><p>

  76.       <code class="command">RETURN NEXT</code> and <code class="command">RETURN

  77.       QUERY</code> do not actually return from the function —

  78.       they simply append zero or more rows to the function's result

  79.       set.  Execution then continues with the next statement in the

  80.       <span class="application">PL/pgSQL</span> function.  As successive

  81.       <code class="command">RETURN NEXT</code> or <code class="command">RETURN

  82.       QUERY</code> commands are executed, the result set is built

  83.       up.  A final <code class="command">RETURN</code>, which should have no

  84.       argument, causes control to exit the function (or you can just

  85.       let control reach the end of the function).

  86.      </p><p>

  87.       <code class="command">RETURN QUERY</code> has a variant

  88.       <code class="command">RETURN QUERY EXECUTE</code>, which specifies the

  89.       query to be executed dynamically.  Parameter expressions can

  90.       be inserted into the computed query string via <code class="literal">USING</code>,

  91.       in just the same way as in the <code class="command">EXECUTE</code> command.

  92.      </p><p>

  93.       If you declared the function with output parameters, write just

  94.       <code class="command">RETURN NEXT</code> with no expression.  On each

  95.       execution, the current values of the output parameter

  96.       variable(s) will be saved for eventual return as a row of the

  97.       result.  Note that you must declare the function as returning

  98.       <code class="literal">SETOF record</code> when there are multiple output

  99.       parameters, or <code class="literal">SETOF <em class="replaceable"><code>sometype</code></em></code>

  100.       when there is just one output parameter of type

  101.       <em class="replaceable"><code>sometype</code></em>, in order to create a set-returning

  102.       function with output parameters.

  103.      </p><p>

  104.       Here is an example of a function using <code class="command">RETURN

  105.       NEXT</code>:

  106. 

  107. </p><pre class="programlisting">

  108. CREATE TABLE foo (fooid INT, foosubid INT, fooname TEXT);

  109. INSERT INTO foo VALUES (1, 2, 'three');

  110. INSERT INTO foo VALUES (4, 5, 'six');

  111. 

  112. CREATE OR REPLACE FUNCTION get_all_foo() RETURNS SETOF foo AS

  113. $BODY$

  114. DECLARE

  115.     r foo%rowtype;

  116. BEGIN

  117.     FOR r IN

  118.         SELECT * FROM foo WHERE fooid &gt; 0

  119.     LOOP

  120.         -- can do some processing here

  121.         RETURN NEXT r; -- return current row of SELECT

  122.     END LOOP;

  123.     RETURN;

  124. END

  125. $BODY$

  126. LANGUAGE plpgsql;

  127. 

  128. SELECT * FROM get_all_foo();

  129. </pre><p>

  130.      </p><p>

  131.       Here is an example of a function using <code class="command">RETURN

  132.       QUERY</code>:

  133. 

  134. </p><pre class="programlisting">

  135. CREATE FUNCTION get_available_flightid(date) RETURNS SETOF integer AS

  136. $BODY$

  137. BEGIN

  138.     RETURN QUERY SELECT flightid

  139.                    FROM flight

  140.                   WHERE flightdate &gt;= $1

  141.                     AND flightdate &lt; ($1 + 1);

  142. 

  143.     -- Since execution is not finished, we can check whether rows were returned

  144.     -- and raise exception if not.

  145.     IF NOT FOUND THEN

  146.         RAISE EXCEPTION 'No flight at %.', $1;

  147.     END IF;

  148. 

  149.     RETURN;

  150.  END

  151. $BODY$

  152. LANGUAGE plpgsql;

  153. 

  154. -- Returns available flights or raises exception if there are no

  155. -- available flights.

  156. SELECT * FROM get_available_flightid(CURRENT_DATE);

  157. </pre><p>

  158.      </p><div class="note"><h3 class="title">Note</h3><p>

  159.        The current implementation of <code class="command">RETURN NEXT</code>

  160.        and <code class="command">RETURN QUERY</code> stores the entire result set

  161.        before returning from the function, as discussed above.  That

  162.        means that if a <span class="application">PL/pgSQL</span> function produces a

  163.        very large result set, performance might be poor: data will be

  164.        written to disk to avoid memory exhaustion, but the function

  165.        itself will not return until the entire result set has been

  166.        generated.  A future version of <span class="application">PL/pgSQL</span> might

  167.        allow users to define set-returning functions

  168.        that do not have this limitation.  Currently, the point at

  169.        which data begins being written to disk is controlled by the

  170.        <a class="xref" href="runtime-config-resource.html#GUC-WORK-MEM">work_mem</a>

  171.        configuration variable.  Administrators who have sufficient

  172.        memory to store larger result sets in memory should consider

  173.        increasing this parameter.

  174.       </p></div></div></div><div class="sect2" id="PLPGSQL-STATEMENTS-RETURNING-PROCEDURE"><div class="titlepage"><div><div><h3 class="title">42.6.2. Returning from a Procedure</h3></div></div></div><p>

  175.      A procedure does not have a return value.  A procedure can therefore end

  176.      without a <code class="command">RETURN</code> statement.  If you wish to use

  177.      a <code class="command">RETURN</code> statement to exit the code early, write

  178.      just <code class="command">RETURN</code> with no expression.

  179.     </p><p>

  180.      If the procedure has output parameters, the final values of the output

  181.      parameter variables will be returned to the caller.

  182.     </p></div><div class="sect2" id="PLPGSQL-STATEMENTS-CALLING-PROCEDURE"><div class="titlepage"><div><div><h3 class="title">42.6.3. Calling a Procedure</h3></div></div></div><p>

  183.      A <span class="application">PL/pgSQL</span> function, procedure,

  184.      or <code class="command">DO</code> block can call a procedure

  185.      using <code class="command">CALL</code>.  Output parameters are handled

  186.      differently from the way that <code class="command">CALL</code> works in plain

  187.      SQL.  Each <code class="literal">INOUT</code> parameter of the procedure must

  188.      correspond to a variable in the <code class="command">CALL</code> statement, and

  189.      whatever the procedure returns is assigned back to that variable after

  190.      it returns.  For example:

  191. </p><pre class="programlisting">

  192. CREATE PROCEDURE triple(INOUT x int)

  193. LANGUAGE plpgsql

  194. AS $$

  195. BEGIN

  196.     x := x * 3;

  197. END;

  198. $$;

  199. 

  200. DO $$

  201. DECLARE myvar int := 5;

  202. BEGIN

  203.   CALL triple(myvar);

  204.   RAISE NOTICE 'myvar = %', myvar;  -- prints 15

  205. END

  206. $$;

  207. </pre><p>

  208.     </p></div><div class="sect2" id="PLPGSQL-CONDITIONALS"><div class="titlepage"><div><div><h3 class="title">42.6.4. Conditionals</h3></div></div></div><p>

  209.      <code class="command">IF</code> and <code class="command">CASE</code> statements let you execute

  210.      alternative commands based on certain conditions.

  211.      <span class="application">PL/pgSQL</span> has three forms of <code class="command">IF</code>:

  212.     </p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"><p><code class="literal">IF ... THEN ... END IF</code></p></li><li class="listitem"><p><code class="literal">IF ... THEN ... ELSE ... END IF</code></p></li><li class="listitem"><p><code class="literal">IF ... THEN ... ELSIF ... THEN ... ELSE ... END IF</code></p></li></ul></div><p>

  213. 

  214.     and two forms of <code class="command">CASE</code>:

  215.     </p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"><p><code class="literal">CASE ... WHEN ... THEN ... ELSE ... END CASE</code></p></li><li class="listitem"><p><code class="literal">CASE WHEN ... THEN ... ELSE ... END CASE</code></p></li></ul></div><p>

  216.     </p><div class="sect3" id="id-1.8.8.8.6.3"><div class="titlepage"><div><div><h4 class="title">42.6.4.1. <code class="literal">IF-THEN</code></h4></div></div></div><pre class="synopsis">

  217. IF <em class="replaceable"><code>boolean-expression</code></em> THEN

  218.     <em class="replaceable"><code>statements</code></em>

  219. END IF;

  220. </pre><p>

  221.         <code class="literal">IF-THEN</code> statements are the simplest form of

  222.         <code class="literal">IF</code>. The statements between

  223.         <code class="literal">THEN</code> and <code class="literal">END IF</code> will be

  224.         executed if the condition is true. Otherwise, they are

  225.         skipped.

  226.        </p><p>

  227.         Example:

  228. </p><pre class="programlisting">

  229. IF v_user_id &lt;&gt; 0 THEN

  230.     UPDATE users SET email = v_email WHERE user_id = v_user_id;

  231. END IF;

  232. </pre><p>

  233.        </p></div><div class="sect3" id="id-1.8.8.8.6.4"><div class="titlepage"><div><div><h4 class="title">42.6.4.2. <code class="literal">IF-THEN-ELSE</code></h4></div></div></div><pre class="synopsis">

  234. IF <em class="replaceable"><code>boolean-expression</code></em> THEN

  235.     <em class="replaceable"><code>statements</code></em>

  236. ELSE

  237.     <em class="replaceable"><code>statements</code></em>

  238. END IF;

  239. </pre><p>

  240.         <code class="literal">IF-THEN-ELSE</code> statements add to

  241.         <code class="literal">IF-THEN</code> by letting you specify an

  242.         alternative set of statements that should be executed if the

  243.         condition is not true.  (Note this includes the case where the

  244.         condition evaluates to NULL.)

  245.        </p><p>

  246.         Examples:

  247. </p><pre class="programlisting">

  248. IF parentid IS NULL OR parentid = ''

  249. THEN

  250.     RETURN fullname;

  251. ELSE

  252.     RETURN hp_true_filename(parentid) || '/' || fullname;

  253. END IF;

  254. </pre><p>

  255. 

  256. </p><pre class="programlisting">

  257. IF v_count &gt; 0 THEN

  258.     INSERT INTO users_count (count) VALUES (v_count);

  259.     RETURN 't';

  260. ELSE

  261.     RETURN 'f';

  262. END IF;

  263. </pre><p>

  264.      </p></div><div class="sect3" id="id-1.8.8.8.6.5"><div class="titlepage"><div><div><h4 class="title">42.6.4.3. <code class="literal">IF-THEN-ELSIF</code></h4></div></div></div><pre class="synopsis">

  265. IF <em class="replaceable"><code>boolean-expression</code></em> THEN

  266.     <em class="replaceable"><code>statements</code></em>

  267. [<span class="optional"> ELSIF <em class="replaceable"><code>boolean-expression</code></em> THEN

  268.     <em class="replaceable"><code>statements</code></em>

  269. [<span class="optional"> ELSIF <em class="replaceable"><code>boolean-expression</code></em> THEN

  270.     <em class="replaceable"><code>statements</code></em>

  271.     ...

  272. </span>]

  273. </span>]

  274. [<span class="optional"> ELSE

  275.     <em class="replaceable"><code>statements</code></em> </span>]

  276. END IF;

  277. </pre><p>

  278.         Sometimes there are more than just two alternatives.

  279.         <code class="literal">IF-THEN-ELSIF</code> provides a convenient

  280.         method of checking several alternatives in turn.

  281.         The <code class="literal">IF</code> conditions are tested successively

  282.         until the first one that is true is found.  Then the

  283.         associated statement(s) are executed, after which control

  284.         passes to the next statement after <code class="literal">END IF</code>.

  285.         (Any subsequent <code class="literal">IF</code> conditions are <span class="emphasis"><em>not</em></span>

  286.         tested.)  If none of the <code class="literal">IF</code> conditions is true,

  287.         then the <code class="literal">ELSE</code> block (if any) is executed.

  288.        </p><p>

  289.         Here is an example:

  290. 

  291. </p><pre class="programlisting">

  292. IF number = 0 THEN

  293.     result := 'zero';

  294. ELSIF number &gt; 0 THEN

  295.     result := 'positive';

  296. ELSIF number &lt; 0 THEN

  297.     result := 'negative';

  298. ELSE

  299.     -- hmm, the only other possibility is that number is null

  300.     result := 'NULL';

  301. END IF;

  302. </pre><p>

  303.        </p><p>

  304.         The key word <code class="literal">ELSIF</code> can also be spelled

  305.         <code class="literal">ELSEIF</code>.

  306.        </p><p>

  307.         An alternative way of accomplishing the same task is to nest

  308.         <code class="literal">IF-THEN-ELSE</code> statements, as in the

  309.         following example:

  310. 

  311. </p><pre class="programlisting">

  312. IF demo_row.sex = 'm' THEN

  313.     pretty_sex := 'man';

  314. ELSE

  315.     IF demo_row.sex = 'f' THEN

  316.         pretty_sex := 'woman';

  317.     END IF;

  318. END IF;

  319. </pre><p>

  320.        </p><p>

  321.         However, this method requires writing a matching <code class="literal">END IF</code>

  322.         for each <code class="literal">IF</code>, so it is much more cumbersome than

  323.         using <code class="literal">ELSIF</code> when there are many alternatives.

  324.        </p></div><div class="sect3" id="id-1.8.8.8.6.6"><div class="titlepage"><div><div><h4 class="title">42.6.4.4. Simple <code class="literal">CASE</code></h4></div></div></div><pre class="synopsis">

  325. CASE <em class="replaceable"><code>search-expression</code></em>

  326.     WHEN <em class="replaceable"><code>expression</code></em> [<span class="optional">, <em class="replaceable"><code>expression</code></em> [<span class="optional"> ... </span>]</span>] THEN

  327.       <em class="replaceable"><code>statements</code></em>

  328.   [<span class="optional"> WHEN <em class="replaceable"><code>expression</code></em> [<span class="optional">, <em class="replaceable"><code>expression</code></em> [<span class="optional"> ... </span>]</span>] THEN

  329.       <em class="replaceable"><code>statements</code></em>

  330.     ... </span>]

  331.   [<span class="optional"> ELSE

  332.       <em class="replaceable"><code>statements</code></em> </span>]

  333. END CASE;

  334. </pre><p>

  335.        The simple form of <code class="command">CASE</code> provides conditional execution

  336.        based on equality of operands.  The <em class="replaceable"><code>search-expression</code></em>

  337.        is evaluated (once) and successively compared to each

  338.        <em class="replaceable"><code>expression</code></em> in the <code class="literal">WHEN</code> clauses.

  339.        If a match is found, then the corresponding

  340.        <em class="replaceable"><code>statements</code></em> are executed, and then control

  341.        passes to the next statement after <code class="literal">END CASE</code>.  (Subsequent

  342.        <code class="literal">WHEN</code> expressions are not evaluated.)  If no match is

  343.        found, the <code class="literal">ELSE</code> <em class="replaceable"><code>statements</code></em> are

  344.        executed; but if <code class="literal">ELSE</code> is not present, then a

  345.        <code class="literal">CASE_NOT_FOUND</code> exception is raised.

  346.       </p><p>

  347.        Here is a simple example:

  348. 

  349. </p><pre class="programlisting">

  350. CASE x

  351.     WHEN 1, 2 THEN

  352.         msg := 'one or two';

  353.     ELSE

  354.         msg := 'other value than one or two';

  355. END CASE;

  356. </pre><p>

  357.       </p></div><div class="sect3" id="id-1.8.8.8.6.7"><div class="titlepage"><div><div><h4 class="title">42.6.4.5. Searched <code class="literal">CASE</code></h4></div></div></div><pre class="synopsis">

  358. CASE

  359.     WHEN <em class="replaceable"><code>boolean-expression</code></em> THEN

  360.       <em class="replaceable"><code>statements</code></em>

  361.   [<span class="optional"> WHEN <em class="replaceable"><code>boolean-expression</code></em> THEN

  362.       <em class="replaceable"><code>statements</code></em>

  363.     ... </span>]

  364.   [<span class="optional"> ELSE

  365.       <em class="replaceable"><code>statements</code></em> </span>]

  366. END CASE;

  367. </pre><p>

  368.        The searched form of <code class="command">CASE</code> provides conditional execution

  369.        based on truth of Boolean expressions.  Each <code class="literal">WHEN</code> clause's

  370.        <em class="replaceable"><code>boolean-expression</code></em> is evaluated in turn,

  371.        until one is found that yields <code class="literal">true</code>.  Then the

  372.        corresponding <em class="replaceable"><code>statements</code></em> are executed, and

  373.        then control passes to the next statement after <code class="literal">END CASE</code>.

  374.        (Subsequent <code class="literal">WHEN</code> expressions are not evaluated.)

  375.        If no true result is found, the <code class="literal">ELSE</code>

  376.        <em class="replaceable"><code>statements</code></em> are executed;

  377.        but if <code class="literal">ELSE</code> is not present, then a

  378.        <code class="literal">CASE_NOT_FOUND</code> exception is raised.

  379.       </p><p>

  380.        Here is an example:

  381. 

  382. </p><pre class="programlisting">

  383. CASE

  384.     WHEN x BETWEEN 0 AND 10 THEN

  385.         msg := 'value is between zero and ten';

  386.     WHEN x BETWEEN 11 AND 20 THEN

  387.         msg := 'value is between eleven and twenty';

  388. END CASE;

  389. </pre><p>

  390.       </p><p>

  391.        This form of <code class="command">CASE</code> is entirely equivalent to

  392.        <code class="literal">IF-THEN-ELSIF</code>, except for the rule that reaching

  393.        an omitted <code class="literal">ELSE</code> clause results in an error rather

  394.        than doing nothing.

  395.       </p></div></div><div class="sect2" id="PLPGSQL-CONTROL-STRUCTURES-LOOPS"><div class="titlepage"><div><div><h3 class="title">42.6.5. Simple Loops</h3></div></div></div><a id="id-1.8.8.8.7.2" class="indexterm"></a><p>

  396.      With the <code class="literal">LOOP</code>, <code class="literal">EXIT</code>,

  397.      <code class="literal">CONTINUE</code>, <code class="literal">WHILE</code>, <code class="literal">FOR</code>,

  398.      and <code class="literal">FOREACH</code> statements, you can arrange for your

  399.      <span class="application">PL/pgSQL</span> function to repeat a series of commands.

  400.     </p><div class="sect3" id="id-1.8.8.8.7.4"><div class="titlepage"><div><div><h4 class="title">42.6.5.1. <code class="literal">LOOP</code></h4></div></div></div><pre class="synopsis">

  401. [<span class="optional"> &lt;&lt;<em class="replaceable"><code>label</code></em>&gt;&gt; </span>]

  402. LOOP

  403.     <em class="replaceable"><code>statements</code></em>

  404. END LOOP [<span class="optional"> <em class="replaceable"><code>label</code></em> </span>];

  405. </pre><p>

  406.       <code class="literal">LOOP</code> defines an unconditional loop that is repeated

  407.       indefinitely until terminated by an <code class="literal">EXIT</code> or

  408.       <code class="command">RETURN</code> statement.  The optional

  409.       <em class="replaceable"><code>label</code></em> can be used by <code class="literal">EXIT</code>

  410.       and <code class="literal">CONTINUE</code> statements within nested loops to

  411.       specify which loop those statements refer to.

  412.      </p></div><div class="sect3" id="id-1.8.8.8.7.5"><div class="titlepage"><div><div><h4 class="title">42.6.5.2. <code class="literal">EXIT</code></h4></div></div></div><a id="id-1.8.8.8.7.5.2" class="indexterm"></a><pre class="synopsis">

  413. EXIT [<span class="optional"> <em class="replaceable"><code>label</code></em> </span>] [<span class="optional"> WHEN <em class="replaceable"><code>boolean-expression</code></em> </span>];

  414. </pre><p>

  415.         If no <em class="replaceable"><code>label</code></em> is given, the innermost

  416.         loop is terminated and the statement following <code class="literal">END

  417.         LOOP</code> is executed next.  If <em class="replaceable"><code>label</code></em>

  418.         is given, it must be the label of the current or some outer

  419.         level of nested loop or block. Then the named loop or block is

  420.         terminated and control continues with the statement after the

  421.         loop's/block's corresponding <code class="literal">END</code>.

  422.        </p><p>

  423.         If <code class="literal">WHEN</code> is specified, the loop exit occurs only if

  424.         <em class="replaceable"><code>boolean-expression</code></em> is true. Otherwise, control passes

  425.         to the statement after <code class="literal">EXIT</code>.

  426.        </p><p>

  427.         <code class="literal">EXIT</code> can be used with all types of loops; it is

  428.         not limited to use with unconditional loops.

  429.        </p><p>

  430.         When used with a

  431.         <code class="literal">BEGIN</code> block, <code class="literal">EXIT</code> passes

  432.         control to the next statement after the end of the block.

  433.         Note that a label must be used for this purpose; an unlabeled

  434.         <code class="literal">EXIT</code> is never considered to match a

  435.         <code class="literal">BEGIN</code> block.  (This is a change from

  436.         pre-8.4 releases of <span class="productname">PostgreSQL</span>, which

  437.         would allow an unlabeled <code class="literal">EXIT</code> to match

  438.         a <code class="literal">BEGIN</code> block.)

  439.        </p><p>

  440.         Examples:

  441. </p><pre class="programlisting">

  442. LOOP

  443.     -- some computations

  444.     IF count &gt; 0 THEN

  445.         EXIT;  -- exit loop

  446.     END IF;

  447. END LOOP;

  448. 

  449. LOOP

  450.     -- some computations

  451.     EXIT WHEN count &gt; 0;  -- same result as previous example

  452. END LOOP;

  453. 

  454. &lt;&lt;ablock&gt;&gt;

  455. BEGIN

  456.     -- some computations

  457.     IF stocks &gt; 100000 THEN

  458.         EXIT ablock;  -- causes exit from the BEGIN block

  459.     END IF;

  460.     -- computations here will be skipped when stocks &gt; 100000

  461. END;

  462. </pre><p>

  463.        </p></div><div class="sect3" id="id-1.8.8.8.7.6"><div class="titlepage"><div><div><h4 class="title">42.6.5.3. <code class="literal">CONTINUE</code></h4></div></div></div><a id="id-1.8.8.8.7.6.2" class="indexterm"></a><pre class="synopsis">

  464. CONTINUE [<span class="optional"> <em class="replaceable"><code>label</code></em> </span>] [<span class="optional"> WHEN <em class="replaceable"><code>boolean-expression</code></em> </span>];

  465. </pre><p>

  466.         If no <em class="replaceable"><code>label</code></em> is given, the next iteration of

  467.         the innermost loop is begun. That is, all statements remaining

  468.         in the loop body are skipped, and control returns

  469.         to the loop control expression (if any) to determine whether

  470.         another loop iteration is needed.

  471.         If <em class="replaceable"><code>label</code></em> is present, it

  472.         specifies the label of the loop whose execution will be

  473.         continued.

  474.        </p><p>

  475.         If <code class="literal">WHEN</code> is specified, the next iteration of the

  476.         loop is begun only if <em class="replaceable"><code>boolean-expression</code></em> is

  477.         true. Otherwise, control passes to the statement after

  478.         <code class="literal">CONTINUE</code>.

  479.        </p><p>

  480.         <code class="literal">CONTINUE</code> can be used with all types of loops; it

  481.         is not limited to use with unconditional loops.

  482.        </p><p>

  483.         Examples:

  484. </p><pre class="programlisting">

  485. LOOP

  486.     -- some computations

  487.     EXIT WHEN count &gt; 100;

  488.     CONTINUE WHEN count &lt; 50;

  489.     -- some computations for count IN [50 .. 100]

  490. END LOOP;

  491. </pre><p>

  492.        </p></div><div class="sect3" id="id-1.8.8.8.7.7"><div class="titlepage"><div><div><h4 class="title">42.6.5.4. <code class="literal">WHILE</code></h4></div></div></div><a id="id-1.8.8.8.7.7.2" class="indexterm"></a><pre class="synopsis">

  493. [<span class="optional"> &lt;&lt;<em class="replaceable"><code>label</code></em>&gt;&gt; </span>]

  494. WHILE <em class="replaceable"><code>boolean-expression</code></em> LOOP

  495.     <em class="replaceable"><code>statements</code></em>

  496. END LOOP [<span class="optional"> <em class="replaceable"><code>label</code></em> </span>];

  497. </pre><p>

  498.         The <code class="literal">WHILE</code> statement repeats a

  499.         sequence of statements so long as the

  500.         <em class="replaceable"><code>boolean-expression</code></em>

  501.         evaluates to true.  The expression is checked just before

  502.         each entry to the loop body.

  503.        </p><p>

  504.         For example:

  505. </p><pre class="programlisting">

  506. WHILE amount_owed &gt; 0 AND gift_certificate_balance &gt; 0 LOOP

  507.     -- some computations here

  508. END LOOP;

  509. 

  510. WHILE NOT done LOOP

  511.     -- some computations here

  512. END LOOP;

  513. </pre><p>

  514.        </p></div><div class="sect3" id="PLPGSQL-INTEGER-FOR"><div class="titlepage"><div><div><h4 class="title">42.6.5.5. <code class="literal">FOR</code> (Integer Variant)</h4></div></div></div><pre class="synopsis">

  515. [<span class="optional"> &lt;&lt;<em class="replaceable"><code>label</code></em>&gt;&gt; </span>]

  516. FOR <em class="replaceable"><code>name</code></em> IN [<span class="optional"> REVERSE </span>] <em class="replaceable"><code>expression</code></em> .. <em class="replaceable"><code>expression</code></em> [<span class="optional"> BY <em class="replaceable"><code>expression</code></em> </span>] LOOP

  517.     <em class="replaceable"><code>statements</code></em>

  518. END LOOP [<span class="optional"> <em class="replaceable"><code>label</code></em> </span>];

  519. </pre><p>

  520.         This form of <code class="literal">FOR</code> creates a loop that iterates over a range

  521.         of integer values. The variable

  522.         <em class="replaceable"><code>name</code></em> is automatically defined as type

  523.         <code class="type">integer</code> and exists only inside the loop (any existing

  524.         definition of the variable name is ignored within the loop).

  525.         The two expressions giving

  526.         the lower and upper bound of the range are evaluated once when entering

  527.         the loop. If the <code class="literal">BY</code> clause isn't specified the iteration

  528.         step is 1, otherwise it's the value specified in the <code class="literal">BY</code>

  529.         clause, which again is evaluated once on loop entry.

  530.         If <code class="literal">REVERSE</code> is specified then the step value is

  531.         subtracted, rather than added, after each iteration.

  532.        </p><p>

  533.         Some examples of integer <code class="literal">FOR</code> loops:

  534. </p><pre class="programlisting">

  535. FOR i IN 1..10 LOOP

  536.     -- i will take on the values 1,2,3,4,5,6,7,8,9,10 within the loop

  537. END LOOP;

  538. 

  539. FOR i IN REVERSE 10..1 LOOP

  540.     -- i will take on the values 10,9,8,7,6,5,4,3,2,1 within the loop

  541. END LOOP;

  542. 

  543. FOR i IN REVERSE 10..1 BY 2 LOOP

  544.     -- i will take on the values 10,8,6,4,2 within the loop

  545. END LOOP;

  546. </pre><p>

  547.        </p><p>

  548.         If the lower bound is greater than the upper bound (or less than,

  549.         in the <code class="literal">REVERSE</code> case), the loop body is not

  550.         executed at all.  No error is raised.

  551.        </p><p>

  552.         If a <em class="replaceable"><code>label</code></em> is attached to the

  553.         <code class="literal">FOR</code> loop then the integer loop variable can be

  554.         referenced with a qualified name, using that

  555.         <em class="replaceable"><code>label</code></em>.

  556.        </p></div></div><div class="sect2" id="PLPGSQL-RECORDS-ITERATING"><div class="titlepage"><div><div><h3 class="title">42.6.6. Looping through Query Results</h3></div></div></div><p>

  557.      Using a different type of <code class="literal">FOR</code> loop, you can iterate through

  558.      the results of a query and manipulate that data

  559.      accordingly. The syntax is:

  560. </p><pre class="synopsis">

  561. [<span class="optional"> &lt;&lt;<em class="replaceable"><code>label</code></em>&gt;&gt; </span>]

  562. FOR <em class="replaceable"><code>target</code></em> IN <em class="replaceable"><code>query</code></em> LOOP

  563.     <em class="replaceable"><code>statements</code></em>

  564. END LOOP [<span class="optional"> <em class="replaceable"><code>label</code></em> </span>];

  565. </pre><p>

  566.      The <em class="replaceable"><code>target</code></em> is a record variable, row variable,

  567.      or comma-separated list of scalar variables.

  568.      The <em class="replaceable"><code>target</code></em> is successively assigned each row

  569.      resulting from the <em class="replaceable"><code>query</code></em> and the loop body is

  570.      executed for each row. Here is an example:

  571. </p><pre class="programlisting">

  572. CREATE FUNCTION refresh_mviews() RETURNS integer AS $$

  573. DECLARE

  574.     mviews RECORD;

  575. BEGIN

  576.     RAISE NOTICE 'Refreshing all materialized views...';

  577. 

  578.     FOR mviews IN

  579.        SELECT n.nspname AS mv_schema,

  580.               c.relname AS mv_name,

  581.               pg_catalog.pg_get_userbyid(c.relowner) AS owner

  582.          FROM pg_catalog.pg_class c

  583.     LEFT JOIN pg_catalog.pg_namespace n ON (n.oid = c.relnamespace)

  584.         WHERE c.relkind = 'm'

  585.      ORDER BY 1

  586.     LOOP

  587. 

  588.         -- Now "mviews" has one record with information about the materialized view

  589. 

  590.         RAISE NOTICE 'Refreshing materialized view %.% (owner: %)...',

  591.                      quote_ident(mviews.mv_schema),

  592.                      quote_ident(mviews.mv_name),

  593.                      quote_ident(mviews.owner);

  594.         EXECUTE format('REFRESH MATERIALIZED VIEW %I.%I', mviews.mv_schema, mviews.mv_name);

  595.     END LOOP;

  596. 

  597.     RAISE NOTICE 'Done refreshing materialized views.';

  598.     RETURN 1;

  599. END;

  600. $$ LANGUAGE plpgsql;

  601. </pre><p>

  602. 

  603.      If the loop is terminated by an <code class="literal">EXIT</code> statement, the last

  604.      assigned row value is still accessible after the loop.

  605.     </p><p>

  606.      The <em class="replaceable"><code>query</code></em> used in this type of <code class="literal">FOR</code>

  607.      statement can be any SQL command that returns rows to the caller:

  608.      <code class="command">SELECT</code> is the most common case,

  609.      but you can also use <code class="command">INSERT</code>, <code class="command">UPDATE</code>, or

  610.      <code class="command">DELETE</code> with a <code class="literal">RETURNING</code> clause.  Some utility

  611.      commands such as <code class="command">EXPLAIN</code> will work too.

  612.     </p><p>

  613.      <span class="application">PL/pgSQL</span> variables are substituted into the query text,

  614.      and the query plan is cached for possible re-use, as discussed in

  615.      detail in <a class="xref" href="plpgsql-implementation.html#PLPGSQL-VAR-SUBST" title="42.11.1. Variable Substitution">Section 42.11.1</a> and

  616.      <a class="xref" href="plpgsql-implementation.html#PLPGSQL-PLAN-CACHING" title="42.11.2. Plan Caching">Section 42.11.2</a>.

  617.     </p><p>

  618.      The <code class="literal">FOR-IN-EXECUTE</code> statement is another way to iterate over

  619.      rows:

  620. </p><pre class="synopsis">

  621. [<span class="optional"> &lt;&lt;<em class="replaceable"><code>label</code></em>&gt;&gt; </span>]

  622. FOR <em class="replaceable"><code>target</code></em> IN EXECUTE <em class="replaceable"><code>text_expression</code></em> [<span class="optional"> USING <em class="replaceable"><code>expression</code></em> [<span class="optional">, ... </span>] </span>] LOOP

  623.     <em class="replaceable"><code>statements</code></em>

  624. END LOOP [<span class="optional"> <em class="replaceable"><code>label</code></em> </span>];

  625. </pre><p>

  626.      This is like the previous form, except that the source query

  627.      is specified as a string expression, which is evaluated and replanned

  628.      on each entry to the <code class="literal">FOR</code> loop.  This allows the programmer to

  629.      choose the speed of a preplanned query or the flexibility of a dynamic

  630.      query, just as with a plain <code class="command">EXECUTE</code> statement.

  631.      As with <code class="command">EXECUTE</code>, parameter values can be inserted

  632.      into the dynamic command via <code class="literal">USING</code>.

  633.     </p><p>

  634.      Another way to specify the query whose results should be iterated

  635.      through is to declare it as a cursor.  This is described in

  636.      <a class="xref" href="plpgsql-cursors.html#PLPGSQL-CURSOR-FOR-LOOP" title="42.7.4. Looping through a Cursor's Result">Section 42.7.4</a>.

  637.     </p></div><div class="sect2" id="PLPGSQL-FOREACH-ARRAY"><div class="titlepage"><div><div><h3 class="title">42.6.7. Looping through Arrays</h3></div></div></div><p>

  638.      The <code class="literal">FOREACH</code> loop is much like a <code class="literal">FOR</code> loop,

  639.      but instead of iterating through the rows returned by a SQL query,

  640.      it iterates through the elements of an array value.

  641.      (In general, <code class="literal">FOREACH</code> is meant for looping through

  642.      components of a composite-valued expression; variants for looping

  643.      through composites besides arrays may be added in future.)

  644.      The <code class="literal">FOREACH</code> statement to loop over an array is:

  645. 

  646. </p><pre class="synopsis">

  647. [<span class="optional"> &lt;&lt;<em class="replaceable"><code>label</code></em>&gt;&gt; </span>]

  648. FOREACH <em class="replaceable"><code>target</code></em> [<span class="optional"> SLICE <em class="replaceable"><code>number</code></em> </span>] IN ARRAY <em class="replaceable"><code>expression</code></em> LOOP

  649.     <em class="replaceable"><code>statements</code></em>

  650. END LOOP [<span class="optional"> <em class="replaceable"><code>label</code></em> </span>];

  651. </pre><p>

  652.     </p><p>

  653.      Without <code class="literal">SLICE</code>, or if <code class="literal">SLICE 0</code> is specified,

  654.      the loop iterates through individual elements of the array produced

  655.      by evaluating the <em class="replaceable"><code>expression</code></em>.

  656.      The <em class="replaceable"><code>target</code></em> variable is assigned each

  657.      element value in sequence, and the loop body is executed for each element.

  658.      Here is an example of looping through the elements of an integer

  659.      array:

  660. 

  661. </p><pre class="programlisting">

  662. CREATE FUNCTION sum(int[]) RETURNS int8 AS $$

  663. DECLARE

  664.   s int8 := 0;

  665.   x int;

  666. BEGIN

  667.   FOREACH x IN ARRAY $1

  668.   LOOP

  669.     s := s + x;

  670.   END LOOP;

  671.   RETURN s;

  672. END;

  673. $$ LANGUAGE plpgsql;

  674. </pre><p>

  675. 

  676.      The elements are visited in storage order, regardless of the number of

  677.      array dimensions.  Although the <em class="replaceable"><code>target</code></em> is

  678.      usually just a single variable, it can be a list of variables when

  679.      looping through an array of composite values (records).  In that case,

  680.      for each array element, the variables are assigned from successive

  681.      columns of the composite value.

  682.     </p><p>

  683.      With a positive <code class="literal">SLICE</code> value, <code class="literal">FOREACH</code>

  684.      iterates through slices of the array rather than single elements.

  685.      The <code class="literal">SLICE</code> value must be an integer constant not larger

  686.      than the number of dimensions of the array.  The

  687.      <em class="replaceable"><code>target</code></em> variable must be an array,

  688.      and it receives successive slices of the array value, where each slice

  689.      is of the number of dimensions specified by <code class="literal">SLICE</code>.

  690.      Here is an example of iterating through one-dimensional slices:

  691. 

  692. </p><pre class="programlisting">

  693. CREATE FUNCTION scan_rows(int[]) RETURNS void AS $$

  694. DECLARE

  695.   x int[];

  696. BEGIN

  697.   FOREACH x SLICE 1 IN ARRAY $1

  698.   LOOP

  699.     RAISE NOTICE 'row = %', x;

  700.   END LOOP;

  701. END;

  702. $$ LANGUAGE plpgsql;

  703. 

  704. SELECT scan_rows(ARRAY[[1,2,3],[4,5,6],[7,8,9],[10,11,12]]);

  705. 

  706. NOTICE:  row = {1,2,3}

  707. NOTICE:  row = {4,5,6}

  708. NOTICE:  row = {7,8,9}

  709. NOTICE:  row = {10,11,12}

  710. </pre><p>

  711.     </p></div><div class="sect2" id="PLPGSQL-ERROR-TRAPPING"><div class="titlepage"><div><div><h3 class="title">42.6.8. Trapping Errors</h3></div></div></div><a id="id-1.8.8.8.10.2" class="indexterm"></a><p>

  712.      By default, any error occurring in a <span class="application">PL/pgSQL</span>

  713.      function aborts execution of the function, and indeed of the

  714.      surrounding transaction as well.  You can trap errors and recover

  715.      from them by using a <code class="command">BEGIN</code> block with an

  716.      <code class="literal">EXCEPTION</code> clause.  The syntax is an extension of the

  717.      normal syntax for a <code class="command">BEGIN</code> block:

  718. 

  719. </p><pre class="synopsis">

  720. [<span class="optional"> &lt;&lt;<em class="replaceable"><code>label</code></em>&gt;&gt; </span>]

  721. [<span class="optional"> DECLARE

  722.     <em class="replaceable"><code>declarations</code></em> </span>]

  723. BEGIN

  724.     <em class="replaceable"><code>statements</code></em>

  725. EXCEPTION

  726.     WHEN <em class="replaceable"><code>condition</code></em> [<span class="optional"> OR <em class="replaceable"><code>condition</code></em> ... </span>] THEN

  727.         <em class="replaceable"><code>handler_statements</code></em>

  728.     [<span class="optional"> WHEN <em class="replaceable"><code>condition</code></em> [<span class="optional"> OR <em class="replaceable"><code>condition</code></em> ... </span>] THEN

  729.           <em class="replaceable"><code>handler_statements</code></em>

  730.       ... </span>]

  731. END;

  732. </pre><p>

  733.     </p><p>

  734.      If no error occurs, this form of block simply executes all the

  735.      <em class="replaceable"><code>statements</code></em>, and then control passes

  736.      to the next statement after <code class="literal">END</code>.  But if an error

  737.      occurs within the <em class="replaceable"><code>statements</code></em>, further

  738.      processing of the <em class="replaceable"><code>statements</code></em> is

  739.      abandoned, and control passes to the <code class="literal">EXCEPTION</code> list.

  740.      The list is searched for the first <em class="replaceable"><code>condition</code></em>

  741.      matching the error that occurred.  If a match is found, the

  742.      corresponding <em class="replaceable"><code>handler_statements</code></em> are

  743.      executed, and then control passes to the next statement after

  744.      <code class="literal">END</code>.  If no match is found, the error propagates out

  745.      as though the <code class="literal">EXCEPTION</code> clause were not there at all:

  746.      the error can be caught by an enclosing block with

  747.      <code class="literal">EXCEPTION</code>, or if there is none it aborts processing

  748.      of the function.

  749.     </p><p>

  750.      The <em class="replaceable"><code>condition</code></em> names can be any of

  751.      those shown in <a class="xref" href="errcodes-appendix.html" title="Appendix A. PostgreSQL Error Codes">Appendix A</a>.  A category

  752.      name matches any error within its category.  The special

  753.      condition name <code class="literal">OTHERS</code> matches every error type except

  754.      <code class="literal">QUERY_CANCELED</code> and <code class="literal">ASSERT_FAILURE</code>.

  755.      (It is possible, but often unwise, to trap those two error types

  756.      by name.)  Condition names are

  757.      not case-sensitive.  Also, an error condition can be specified

  758.      by <code class="literal">SQLSTATE</code> code; for example these are equivalent:

  759. </p><pre class="programlisting">

  760. WHEN division_by_zero THEN ...

  761. WHEN SQLSTATE '22012' THEN ...

  762. </pre><p>

  763.     </p><p>

  764.      If a new error occurs within the selected

  765.      <em class="replaceable"><code>handler_statements</code></em>, it cannot be caught

  766.      by this <code class="literal">EXCEPTION</code> clause, but is propagated out.

  767.      A surrounding <code class="literal">EXCEPTION</code> clause could catch it.

  768.     </p><p>

  769.      When an error is caught by an <code class="literal">EXCEPTION</code> clause,

  770.      the local variables of the <span class="application">PL/pgSQL</span> function

  771.      remain as they were when the error occurred, but all changes

  772.      to persistent database state within the block are rolled back.

  773.      As an example, consider this fragment:

  774. 

  775. </p><pre class="programlisting">

  776. INSERT INTO mytab(firstname, lastname) VALUES('Tom', 'Jones');

  777. BEGIN

  778.     UPDATE mytab SET firstname = 'Joe' WHERE lastname = 'Jones';

  779.     x := x + 1;

  780.     y := x / 0;

  781. EXCEPTION

  782.     WHEN division_by_zero THEN

  783.         RAISE NOTICE 'caught division_by_zero';

  784.         RETURN x;

  785. END;

  786. </pre><p>

  787. 

  788.      When control reaches the assignment to <code class="literal">y</code>, it will

  789.      fail with a <code class="literal">division_by_zero</code> error.  This will be caught by

  790.      the <code class="literal">EXCEPTION</code> clause.  The value returned in the

  791.      <code class="command">RETURN</code> statement will be the incremented value of

  792.      <code class="literal">x</code>, but the effects of the <code class="command">UPDATE</code> command will

  793.      have been rolled back.  The <code class="command">INSERT</code> command preceding the

  794.      block is not rolled back, however, so the end result is that the database

  795.      contains <code class="literal">Tom Jones</code> not <code class="literal">Joe Jones</code>.

  796.     </p><div class="tip"><h3 class="title">Tip</h3><p>

  797.       A block containing an <code class="literal">EXCEPTION</code> clause is significantly

  798.       more expensive to enter and exit than a block without one.  Therefore,

  799.       don't use <code class="literal">EXCEPTION</code> without need.

  800.      </p></div><div class="example" id="PLPGSQL-UPSERT-EXAMPLE"><p class="title"><strong>Example 42.2. Exceptions with <code class="command">UPDATE</code>/<code class="command">INSERT</code></strong></p><div class="example-contents"><p>

  801. 

  802.     This example uses exception handling to perform either

  803.     <code class="command">UPDATE</code> or <code class="command">INSERT</code>, as appropriate.  It is

  804.     recommended that applications use <code class="command">INSERT</code> with

  805.     <code class="literal">ON CONFLICT DO UPDATE</code> rather than actually using

  806.     this pattern.  This example serves primarily to illustrate use of

  807.     <span class="application">PL/pgSQL</span> control flow structures:

  808. 

  809. </p><pre class="programlisting">

  810. CREATE TABLE db (a INT PRIMARY KEY, b TEXT);

  811. 

  812. CREATE FUNCTION merge_db(key INT, data TEXT) RETURNS VOID AS

  813. $$

  814. BEGIN

  815.     LOOP

  816.         -- first try to update the key

  817.         UPDATE db SET b = data WHERE a = key;

  818.         IF found THEN

  819.             RETURN;

  820.         END IF;

  821.         -- not there, so try to insert the key

  822.         -- if someone else inserts the same key concurrently,

  823.         -- we could get a unique-key failure

  824.         BEGIN

  825.             INSERT INTO db(a,b) VALUES (key, data);

  826.             RETURN;

  827.         EXCEPTION WHEN unique_violation THEN

  828.             -- Do nothing, and loop to try the UPDATE again.

  829.         END;

  830.     END LOOP;

  831. END;

  832. $$

  833. LANGUAGE plpgsql;

  834. 

  835. SELECT merge_db(1, 'david');

  836. SELECT merge_db(1, 'dennis');

  837. </pre><p>

  838. 

  839.      This coding assumes the <code class="literal">unique_violation</code> error is caused by

  840.      the <code class="command">INSERT</code>, and not by, say, an <code class="command">INSERT</code> in a

  841.      trigger function on the table.  It might also misbehave if there is

  842.      more than one unique index on the table, since it will retry the

  843.      operation regardless of which index caused the error.

  844.      More safety could be had by using the

  845.      features discussed next to check that the trapped error was the one

  846.      expected.

  847.     </p></div></div><br class="example-break" /><div class="sect3" id="PLPGSQL-EXCEPTION-DIAGNOSTICS"><div class="titlepage"><div><div><h4 class="title">42.6.8.1. Obtaining Information about an Error</h4></div></div></div><p>

  848.      Exception handlers frequently need to identify the specific error that

  849.      occurred.  There are two ways to get information about the current

  850.      exception in <span class="application">PL/pgSQL</span>: special variables and the

  851.      <code class="command">GET STACKED DIAGNOSTICS</code> command.

  852.     </p><p>

  853.      Within an exception handler, the special variable

  854.      <code class="varname">SQLSTATE</code> contains the error code that corresponds to

  855.      the exception that was raised (refer to <a class="xref" href="errcodes-appendix.html#ERRCODES-TABLE" title="Table A.1. PostgreSQL Error Codes">Table A.1</a>

  856.      for a list of possible error codes). The special variable

  857.      <code class="varname">SQLERRM</code> contains the error message associated with the

  858.      exception. These variables are undefined outside exception handlers.

  859.     </p><p>

  860.      Within an exception handler, one may also retrieve

  861.      information about the current exception by using the

  862.      <code class="command">GET STACKED DIAGNOSTICS</code> command, which has the form:

  863. 

  864. </p><pre class="synopsis">

  865. GET STACKED DIAGNOSTICS <em class="replaceable"><code>variable</code></em> { = | := } <em class="replaceable"><code>item</code></em> [<span class="optional"> , ... </span>];

  866. </pre><p>

  867. 

  868.      Each <em class="replaceable"><code>item</code></em> is a key word identifying a status

  869.      value to be assigned to the specified <em class="replaceable"><code>variable</code></em>

  870.      (which should be of the right data type to receive it).  The currently

  871.      available status items are shown

  872.      in <a class="xref" href="plpgsql-control-structures.html#PLPGSQL-EXCEPTION-DIAGNOSTICS-VALUES" title="Table 42.2. Error Diagnostics Items">Table 42.2</a>.

  873.     </p><div class="table" id="PLPGSQL-EXCEPTION-DIAGNOSTICS-VALUES"><p class="title"><strong>Table 42.2. Error Diagnostics Items</strong></p><div class="table-contents"><table class="table" summary="Error Diagnostics Items" border="1"><colgroup><col /><col /><col /></colgroup><thead><tr><th>Name</th><th>Type</th><th>Description</th></tr></thead><tbody><tr><td><code class="literal">RETURNED_SQLSTATE</code></td><td><code class="type">text</code></td><td>the SQLSTATE error code of the exception</td></tr><tr><td><code class="literal">COLUMN_NAME</code></td><td><code class="type">text</code></td><td>the name of the column related to exception</td></tr><tr><td><code class="literal">CONSTRAINT_NAME</code></td><td><code class="type">text</code></td><td>the name of the constraint related to exception</td></tr><tr><td><code class="literal">PG_DATATYPE_NAME</code></td><td><code class="type">text</code></td><td>the name of the data type related to exception</td></tr><tr><td><code class="literal">MESSAGE_TEXT</code></td><td><code class="type">text</code></td><td>the text of the exception's primary message</td></tr><tr><td><code class="literal">TABLE_NAME</code></td><td><code class="type">text</code></td><td>the name of the table related to exception</td></tr><tr><td><code class="literal">SCHEMA_NAME</code></td><td><code class="type">text</code></td><td>the name of the schema related to exception</td></tr><tr><td><code class="literal">PG_EXCEPTION_DETAIL</code></td><td><code class="type">text</code></td><td>the text of the exception's detail message, if any</td></tr><tr><td><code class="literal">PG_EXCEPTION_HINT</code></td><td><code class="type">text</code></td><td>the text of the exception's hint message, if any</td></tr><tr><td><code class="literal">PG_EXCEPTION_CONTEXT</code></td><td><code class="type">text</code></td><td>line(s) of text describing the call stack at the time of the

  874.           exception (see <a class="xref" href="plpgsql-control-structures.html#PLPGSQL-CALL-STACK" title="42.6.9. Obtaining Execution Location Information">Section 42.6.9</a>)</td></tr></tbody></table></div></div><br class="table-break" /><p>

  875.      If the exception did not set a value for an item, an empty string

  876.      will be returned.

  877.     </p><p>

  878.      Here is an example:

  879. </p><pre class="programlisting">

  880. DECLARE

  881.   text_var1 text;

  882.   text_var2 text;

  883.   text_var3 text;

  884. BEGIN

  885.   -- some processing which might cause an exception

  886.   ...

  887. EXCEPTION WHEN OTHERS THEN

  888.   GET STACKED DIAGNOSTICS text_var1 = MESSAGE_TEXT,

  889.                           text_var2 = PG_EXCEPTION_DETAIL,

  890.                           text_var3 = PG_EXCEPTION_HINT;

  891. END;

  892. </pre><p>

  893.     </p></div></div><div class="sect2" id="PLPGSQL-CALL-STACK"><div class="titlepage"><div><div><h3 class="title">42.6.9. Obtaining Execution Location Information</h3></div></div></div><p>

  894.     The <code class="command">GET DIAGNOSTICS</code> command, previously described

  895.     in <a class="xref" href="plpgsql-statements.html#PLPGSQL-STATEMENTS-DIAGNOSTICS" title="42.5.5. Obtaining the Result Status">Section 42.5.5</a>, retrieves information

  896.     about current execution state (whereas the <code class="command">GET STACKED

  897.     DIAGNOSTICS</code> command discussed above reports information about

  898.     the execution state as of a previous error).  Its <code class="literal">PG_CONTEXT</code>

  899.     status item is useful for identifying the current execution

  900.     location.  <code class="literal">PG_CONTEXT</code> returns a text string with line(s)

  901.     of text describing the call stack.  The first line refers to the current

  902.     function and currently executing <code class="command">GET DIAGNOSTICS</code>

  903.     command.  The second and any subsequent lines refer to calling functions

  904.     further up the call stack.  For example:

  905. 

  906. </p><pre class="programlisting">

  907. CREATE OR REPLACE FUNCTION outer_func() RETURNS integer AS $$

  908. BEGIN

  909.   RETURN inner_func();

  910. END;

  911. $$ LANGUAGE plpgsql;

  912. 

  913. CREATE OR REPLACE FUNCTION inner_func() RETURNS integer AS $$

  914. DECLARE

  915.   stack text;

  916. BEGIN

  917.   GET DIAGNOSTICS stack = PG_CONTEXT;

  918.   RAISE NOTICE E'--- Call Stack ---\n%', stack;

  919.   RETURN 1;

  920. END;

  921. $$ LANGUAGE plpgsql;

  922. 

  923. SELECT outer_func();

  924. 

  925. NOTICE:  --- Call Stack ---

  926. PL/pgSQL function inner_func() line 5 at GET DIAGNOSTICS

  927. PL/pgSQL function outer_func() line 3 at RETURN

  928. CONTEXT:  PL/pgSQL function outer_func() line 3 at RETURN

  929.  outer_func

  930.  ------------

  931.            1

  932. (1 row)

  933. </pre><p>

  934. 

  935.    </p><p>

  936.     <code class="literal">GET STACKED DIAGNOSTICS ... PG_EXCEPTION_CONTEXT</code>

  937.     returns the same sort of stack trace, but describing the location

  938.     at which an error was detected, rather than the current location.

  939.    </p></div></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="plpgsql-statements.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="plpgsql.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="plpgsql-cursors.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">42.5. Basic Statements </td><td width="20%" align="center"><a accesskey="h" href="index.html">Home</a></td><td width="40%" align="right" valign="top"> 42.7. Cursors</td></tr></table></div></body></html>
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