Baoding-FenShuaJiang
/
Green_GoodERP18_FSJ_Standard


			
				
					
						
						
							
							<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<!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>4.3. Calling Functions</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="sql-expressions.html" title="4.2. Value Expressions" /><link rel="next" href="ddl.html" title="Chapter 5. Data Definition" /></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">4.3. Calling Functions</th></tr><tr><td width="10%" align="left"><a accesskey="p" href="sql-expressions.html" title="4.2. Value Expressions">Prev</a> </td><td width="10%" align="left"><a accesskey="u" href="sql-syntax.html" title="Chapter 4. SQL Syntax">Up</a></td><th width="60%" align="center">Chapter 4. SQL Syntax</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="ddl.html" title="Chapter 5. Data Definition">Next</a></td></tr></table><hr></hr></div><div class="sect1" id="SQL-SYNTAX-CALLING-FUNCS"><div class="titlepage"><div><div><h2 class="title" style="clear: both">4.3. Calling Functions</h2></div></div></div><div class="toc"><dl class="toc"><dt><span class="sect2"><a href="sql-syntax-calling-funcs.html#SQL-SYNTAX-CALLING-FUNCS-POSITIONAL">4.3.1. Using Positional Notation</a></span></dt><dt><span class="sect2"><a href="sql-syntax-calling-funcs.html#SQL-SYNTAX-CALLING-FUNCS-NAMED">4.3.2. Using Named Notation</a></span></dt><dt><span class="sect2"><a href="sql-syntax-calling-funcs.html#SQL-SYNTAX-CALLING-FUNCS-MIXED">4.3.3. Using Mixed Notation</a></span></dt></dl></div><a id="id-1.5.3.7.2" class="indexterm"></a><p>
    <span class="productname">PostgreSQL</span> allows functions that have named
    parameters to be called using either <em class="firstterm">positional</em> or
    <em class="firstterm">named</em> notation.  Named notation is especially
    useful for functions that have a large number of parameters, since it
    makes the associations between parameters and actual arguments more
    explicit and reliable.
    In positional notation, a function call is written with
    its argument values in the same order as they are defined in the function
    declaration.  In named notation, the arguments are matched to the
    function parameters by name and can be written in any order.
    For each notation, also consider the effect of function argument types,
    documented in <a class="xref" href="typeconv-func.html" title="10.3. Functions">Section 10.3</a>.
   </p><p>
    In either notation, parameters that have default values given in the
    function declaration need not be written in the call at all.  But this
    is particularly useful in named notation, since any combination of
    parameters can be omitted; while in positional notation parameters can
    only be omitted from right to left.
   </p><p>
    <span class="productname">PostgreSQL</span> also supports
    <em class="firstterm">mixed</em> notation, which combines positional and
    named notation.  In this case, positional parameters are written first
    and named parameters appear after them.
   </p><p>
    The following examples will illustrate the usage of all three
    notations, using the following function definition:
</p><pre class="programlisting">
CREATE FUNCTION concat_lower_or_upper(a text, b text, uppercase boolean DEFAULT false)
RETURNS text
AS
$$
 SELECT CASE
        WHEN $3 THEN UPPER($1 || ' ' || $2)
        ELSE LOWER($1 || ' ' || $2)
        END;
$$
LANGUAGE SQL IMMUTABLE STRICT;
</pre><p>
    Function <code class="function">concat_lower_or_upper</code> has two mandatory
    parameters, <code class="literal">a</code> and <code class="literal">b</code>.  Additionally
    there is one optional parameter <code class="literal">uppercase</code> which defaults
    to <code class="literal">false</code>.  The <code class="literal">a</code> and
    <code class="literal">b</code> inputs will be concatenated, and forced to either
    upper or lower case depending on the <code class="literal">uppercase</code>
    parameter.  The remaining details of this function
    definition are not important here (see <a class="xref" href="extend.html" title="Chapter 37. Extending SQL">Chapter 37</a> for
    more information).
   </p><div class="sect2" id="SQL-SYNTAX-CALLING-FUNCS-POSITIONAL"><div class="titlepage"><div><div><h3 class="title">4.3.1. Using Positional Notation</h3></div></div></div><a id="id-1.5.3.7.7.2" class="indexterm"></a><p>
     Positional notation is the traditional mechanism for passing arguments
     to functions in <span class="productname">PostgreSQL</span>.  An example is:
</p><pre class="screen">
SELECT concat_lower_or_upper('Hello', 'World', true);
 concat_lower_or_upper 
-----------------------
 HELLO WORLD
(1 row)
</pre><p>
     All arguments are specified in order.  The result is upper case since
     <code class="literal">uppercase</code> is specified as <code class="literal">true</code>.
     Another example is:
</p><pre class="screen">
SELECT concat_lower_or_upper('Hello', 'World');
 concat_lower_or_upper 
-----------------------
 hello world
(1 row)
</pre><p>
     Here, the <code class="literal">uppercase</code> parameter is omitted, so it
     receives its default value of <code class="literal">false</code>, resulting in
     lower case output.  In positional notation, arguments can be omitted
     from right to left so long as they have defaults.
    </p></div><div class="sect2" id="SQL-SYNTAX-CALLING-FUNCS-NAMED"><div class="titlepage"><div><div><h3 class="title">4.3.2. Using Named Notation</h3></div></div></div><a id="id-1.5.3.7.8.2" class="indexterm"></a><p>
     In named notation, each argument's name is specified using
     <code class="literal">=&gt;</code> to separate it from the argument expression.
     For example:
</p><pre class="screen">
SELECT concat_lower_or_upper(a =&gt; 'Hello', b =&gt; 'World');
 concat_lower_or_upper 
-----------------------
 hello world
(1 row)
</pre><p>
     Again, the argument <code class="literal">uppercase</code> was omitted
     so it is set to <code class="literal">false</code> implicitly.  One advantage of
     using named notation is that the arguments may be specified in any
     order, for example:
</p><pre class="screen">
SELECT concat_lower_or_upper(a =&gt; 'Hello', b =&gt; 'World', uppercase =&gt; true);
 concat_lower_or_upper 
-----------------------
 HELLO WORLD
(1 row)

SELECT concat_lower_or_upper(a =&gt; 'Hello', uppercase =&gt; true, b =&gt; 'World');
 concat_lower_or_upper 
-----------------------
 HELLO WORLD
(1 row)
</pre><p>
    </p><p>
      An older syntax based on ":=" is supported for backward compatibility:
</p><pre class="screen">
SELECT concat_lower_or_upper(a := 'Hello', uppercase := true, b := 'World');
 concat_lower_or_upper 
-----------------------
 HELLO WORLD
(1 row)
</pre><p>
    </p></div><div class="sect2" id="SQL-SYNTAX-CALLING-FUNCS-MIXED"><div class="titlepage"><div><div><h3 class="title">4.3.3. Using Mixed Notation</h3></div></div></div><a id="id-1.5.3.7.9.2" class="indexterm"></a><p>
    The mixed notation combines positional and named notation. However, as
    already mentioned, named arguments cannot precede positional arguments.
    For example:
</p><pre class="screen">
SELECT concat_lower_or_upper('Hello', 'World', uppercase =&gt; true);
 concat_lower_or_upper 
-----------------------
 HELLO WORLD
(1 row)
</pre><p>
    In the above query, the arguments <code class="literal">a</code> and
    <code class="literal">b</code> are specified positionally, while
    <code class="literal">uppercase</code> is specified by name.  In this example,
    that adds little except documentation.  With a more complex function
    having numerous parameters that have default values, named or mixed
    notation can save a great deal of writing and reduce chances for error.
   </p><div class="note"><h3 class="title">Note</h3><p>
     Named and mixed call notations currently cannot be used when calling an
     aggregate function (but they do work when an aggregate function is used
     as a window function).
    </p></div></div></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="sql-expressions.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="sql-syntax.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="ddl.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">4.2. Value Expressions </td><td width="20%" align="center"><a accesskey="h" href="index.html">Home</a></td><td width="40%" align="right" valign="top"> Chapter 5. Data Definition</td></tr></table></div></body></html>