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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>36.17. columns</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="infoschema-column-udt-usage.html" title="36.16. column_udt_usage" /><link rel="next" href="infoschema-constraint-column-usage.html" title="36.18. constraint_column_usage" /></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">36.17. <code xmlns="http://www.w3.org/1999/xhtml" class="literal">columns</code></th></tr><tr><td width="10%" align="left"><a accesskey="p" href="infoschema-column-udt-usage.html" title="36.16. column_udt_usage">Prev</a> </td><td width="10%" align="left"><a accesskey="u" href="information-schema.html" title="Chapter 36. The Information Schema">Up</a></td><th width="60%" align="center">Chapter 36. The Information Schema</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="infoschema-constraint-column-usage.html" title="36.18. constraint_column_usage">Next</a></td></tr></table><hr></hr></div><div class="sect1" id="INFOSCHEMA-COLUMNS"><div class="titlepage"><div><div><h2 class="title" style="clear: both">36.17. <code class="literal">columns</code></h2></div></div></div><p>

  3.    The view <code class="literal">columns</code> contains information about all

  4.    table columns (or view columns) in the database.  System columns

  5.    (<code class="literal">ctid</code>, etc.) are not included.  Only those columns are

  6.    shown that the current user has access to (by way of being the

  7.    owner or having some privilege).

  8.   </p><div class="table" id="id-1.7.6.21.3"><p class="title"><strong>Table 36.15. <code class="literal">columns</code> Columns</strong></p><div class="table-contents"><table class="table" summary="columns Columns" border="1"><colgroup><col /><col /><col /></colgroup><thead><tr><th>Name</th><th>Data Type</th><th>Description</th></tr></thead><tbody><tr><td><code class="literal">table_catalog</code></td><td><code class="type">sql_identifier</code></td><td>Name of the database containing the table (always the current database)</td></tr><tr><td><code class="literal">table_schema</code></td><td><code class="type">sql_identifier</code></td><td>Name of the schema containing the table</td></tr><tr><td><code class="literal">table_name</code></td><td><code class="type">sql_identifier</code></td><td>Name of the table</td></tr><tr><td><code class="literal">column_name</code></td><td><code class="type">sql_identifier</code></td><td>Name of the column</td></tr><tr><td><code class="literal">ordinal_position</code></td><td><code class="type">cardinal_number</code></td><td>Ordinal position of the column within the table (count starts at 1)</td></tr><tr><td><code class="literal">column_default</code></td><td><code class="type">character_data</code></td><td>Default expression of the column</td></tr><tr><td><code class="literal">is_nullable</code></td><td><code class="type">yes_or_no</code></td><td>

  9.        <code class="literal">YES</code> if the column is possibly nullable,

  10.        <code class="literal">NO</code> if it is known not nullable.  A not-null

  11.        constraint is one way a column can be known not nullable, but

  12.        there can be others.

  13.       </td></tr><tr><td><code class="literal">data_type</code></td><td><code class="type">character_data</code></td><td>

  14.        Data type of the column, if it is a built-in type, or

  15.        <code class="literal">ARRAY</code> if it is some array (in that case, see

  16.        the view <code class="literal">element_types</code>), else

  17.        <code class="literal">USER-DEFINED</code> (in that case, the type is

  18.        identified in <code class="literal">udt_name</code> and associated

  19.        columns).  If the column is based on a domain, this column

  20.        refers to the type underlying the domain (and the domain is

  21.        identified in <code class="literal">domain_name</code> and associated

  22.        columns).

  23.       </td></tr><tr><td><code class="literal">character_maximum_length</code></td><td><code class="type">cardinal_number</code></td><td>

  24.        If <code class="literal">data_type</code> identifies a character or bit

  25.        string type, the declared maximum length; null for all other

  26.        data types or if no maximum length was declared.

  27.       </td></tr><tr><td><code class="literal">character_octet_length</code></td><td><code class="type">cardinal_number</code></td><td>

  28.        If <code class="literal">data_type</code> identifies a character type,

  29.        the maximum possible length in octets (bytes) of a datum; null

  30.        for all other data types.  The maximum octet length depends on

  31.        the declared character maximum length (see above) and the

  32.        server encoding.

  33.       </td></tr><tr><td><code class="literal">numeric_precision</code></td><td><code class="type">cardinal_number</code></td><td>

  34.        If <code class="literal">data_type</code> identifies a numeric type, this

  35.        column contains the (declared or implicit) precision of the

  36.        type for this column.  The precision indicates the number of

  37.        significant digits.  It can be expressed in decimal (base 10)

  38.        or binary (base 2) terms, as specified in the column

  39.        <code class="literal">numeric_precision_radix</code>.  For all other data

  40.        types, this column is null.

  41.       </td></tr><tr><td><code class="literal">numeric_precision_radix</code></td><td><code class="type">cardinal_number</code></td><td>

  42.        If <code class="literal">data_type</code> identifies a numeric type, this

  43.        column indicates in which base the values in the columns

  44.        <code class="literal">numeric_precision</code> and

  45.        <code class="literal">numeric_scale</code> are expressed.  The value is

  46.        either 2 or 10.  For all other data types, this column is null.

  47.       </td></tr><tr><td><code class="literal">numeric_scale</code></td><td><code class="type">cardinal_number</code></td><td>

  48.        If <code class="literal">data_type</code> identifies an exact numeric

  49.        type, this column contains the (declared or implicit) scale of

  50.        the type for this column.  The scale indicates the number of

  51.        significant digits to the right of the decimal point.  It can

  52.        be expressed in decimal (base 10) or binary (base 2) terms, as

  53.        specified in the column

  54.        <code class="literal">numeric_precision_radix</code>.  For all other data

  55.        types, this column is null.

  56.       </td></tr><tr><td><code class="literal">datetime_precision</code></td><td><code class="type">cardinal_number</code></td><td>

  57.        If <code class="literal">data_type</code> identifies a date, time,

  58.        timestamp, or interval type, this column contains the (declared

  59.        or implicit) fractional seconds precision of the type for this

  60.        column, that is, the number of decimal digits maintained

  61.        following the decimal point in the seconds value.  For all

  62.        other data types, this column is null.

  63.       </td></tr><tr><td><code class="literal">interval_type</code></td><td><code class="type">character_data</code></td><td>

  64.        If <code class="literal">data_type</code> identifies an interval type,

  65.        this column contains the specification which fields the

  66.        intervals include for this column, e.g., <code class="literal">YEAR TO

  67.        MONTH</code>, <code class="literal">DAY TO SECOND</code>, etc.  If no

  68.        field restrictions were specified (that is, the interval

  69.        accepts all fields), and for all other data types, this field

  70.        is null.

  71.       </td></tr><tr><td><code class="literal">interval_precision</code></td><td><code class="type">cardinal_number</code></td><td>

  72.        Applies to a feature not available

  73.        in <span class="productname">PostgreSQL</span>

  74.        (see <code class="literal">datetime_precision</code> for the fractional

  75.        seconds precision of interval type columns)

  76.       </td></tr><tr><td><code class="literal">character_set_catalog</code></td><td><code class="type">sql_identifier</code></td><td>Applies to a feature not available in <span class="productname">PostgreSQL</span></td></tr><tr><td><code class="literal">character_set_schema</code></td><td><code class="type">sql_identifier</code></td><td>Applies to a feature not available in <span class="productname">PostgreSQL</span></td></tr><tr><td><code class="literal">character_set_name</code></td><td><code class="type">sql_identifier</code></td><td>Applies to a feature not available in <span class="productname">PostgreSQL</span></td></tr><tr><td><code class="literal">collation_catalog</code></td><td><code class="type">sql_identifier</code></td><td>

  77.        Name of the database containing the collation of the column

  78.        (always the current database), null if default or the data type

  79.        of the column is not collatable

  80.       </td></tr><tr><td><code class="literal">collation_schema</code></td><td><code class="type">sql_identifier</code></td><td>

  81.        Name of the schema containing the collation of the column, null

  82.        if default or the data type of the column is not collatable

  83.       </td></tr><tr><td><code class="literal">collation_name</code></td><td><code class="type">sql_identifier</code></td><td>

  84.        Name of the collation of the column, null if default or the

  85.        data type of the column is not collatable

  86.       </td></tr><tr><td><code class="literal">domain_catalog</code></td><td><code class="type">sql_identifier</code></td><td>

  87.        If the column has a domain type, the name of the database that

  88.        the domain is defined in (always the current database), else

  89.        null.

  90.       </td></tr><tr><td><code class="literal">domain_schema</code></td><td><code class="type">sql_identifier</code></td><td>

  91.        If the column has a domain type, the name of the schema that

  92.        the domain is defined in, else null.

  93.       </td></tr><tr><td><code class="literal">domain_name</code></td><td><code class="type">sql_identifier</code></td><td>If the column has a domain type, the name of the domain, else null.</td></tr><tr><td><code class="literal">udt_catalog</code></td><td><code class="type">sql_identifier</code></td><td>

  94.        Name of the database that the column data type (the underlying

  95.        type of the domain, if applicable) is defined in (always the

  96.        current database)

  97.       </td></tr><tr><td><code class="literal">udt_schema</code></td><td><code class="type">sql_identifier</code></td><td>

  98.        Name of the schema that the column data type (the underlying

  99.        type of the domain, if applicable) is defined in

  100.       </td></tr><tr><td><code class="literal">udt_name</code></td><td><code class="type">sql_identifier</code></td><td>

  101.        Name of the column data type (the underlying type of the

  102.        domain, if applicable)

  103.       </td></tr><tr><td><code class="literal">scope_catalog</code></td><td><code class="type">sql_identifier</code></td><td>Applies to a feature not available in <span class="productname">PostgreSQL</span></td></tr><tr><td><code class="literal">scope_schema</code></td><td><code class="type">sql_identifier</code></td><td>Applies to a feature not available in <span class="productname">PostgreSQL</span></td></tr><tr><td><code class="literal">scope_name</code></td><td><code class="type">sql_identifier</code></td><td>Applies to a feature not available in <span class="productname">PostgreSQL</span></td></tr><tr><td><code class="literal">maximum_cardinality</code></td><td><code class="type">cardinal_number</code></td><td>Always null, because arrays always have unlimited maximum cardinality in <span class="productname">PostgreSQL</span></td></tr><tr><td><code class="literal">dtd_identifier</code></td><td><code class="type">sql_identifier</code></td><td>

  104.        An identifier of the data type descriptor of the column, unique

  105.        among the data type descriptors pertaining to the table.  This

  106.        is mainly useful for joining with other instances of such

  107.        identifiers.  (The specific format of the identifier is not

  108.        defined and not guaranteed to remain the same in future

  109.        versions.)

  110.       </td></tr><tr><td><code class="literal">is_self_referencing</code></td><td><code class="type">yes_or_no</code></td><td>Applies to a feature not available in <span class="productname">PostgreSQL</span></td></tr><tr><td><code class="literal">is_identity</code></td><td><code class="type">yes_or_no</code></td><td>

  111.        If the column is an identity column, then <code class="literal">YES</code>,

  112.        else <code class="literal">NO</code>.

  113.       </td></tr><tr><td><code class="literal">identity_generation</code></td><td><code class="type">character_data</code></td><td>

  114.        If the column is an identity column, then <code class="literal">ALWAYS</code>

  115.        or <code class="literal">BY DEFAULT</code>, reflecting the definition of the

  116.        column.

  117.       </td></tr><tr><td><code class="literal">identity_start</code></td><td><code class="type">character_data</code></td><td>

  118.        If the column is an identity column, then the start value of the

  119.        internal sequence, else null.

  120.       </td></tr><tr><td><code class="literal">identity_increment</code></td><td><code class="type">character_data</code></td><td>

  121.        If the column is an identity column, then the increment of the internal

  122.        sequence, else null.

  123.       </td></tr><tr><td><code class="literal">identity_maximum</code></td><td><code class="type">character_data</code></td><td>

  124.        If the column is an identity column, then the maximum value of the

  125.        internal sequence, else null.

  126.       </td></tr><tr><td><code class="literal">identity_minimum</code></td><td><code class="type">character_data</code></td><td>

  127.        If the column is an identity column, then the minimum value of the

  128.        internal sequence, else null.

  129.       </td></tr><tr><td><code class="literal">identity_cycle</code></td><td><code class="type">yes_or_no</code></td><td>

  130.        If the column is an identity column, then <code class="literal">YES</code> if the

  131.        internal sequence cycles or <code class="literal">NO</code> if it does not;

  132.        otherwise null.

  133.       </td></tr><tr><td><code class="literal">is_generated</code></td><td><code class="type">character_data</code></td><td>

  134.        If the column is a generated column, then <code class="literal">ALWAYS</code>,

  135.        else <code class="literal">NEVER</code>.

  136.       </td></tr><tr><td><code class="literal">generation_expression</code></td><td><code class="type">character_data</code></td><td>

  137.        If the column is a generated column, then the generation expression,

  138.        else null.

  139.       </td></tr><tr><td><code class="literal">is_updatable</code></td><td><code class="type">yes_or_no</code></td><td>

  140.        <code class="literal">YES</code> if the column is updatable,

  141.        <code class="literal">NO</code> if not (Columns in base tables are always

  142.        updatable, columns in views not necessarily)

  143.       </td></tr></tbody></table></div></div><br class="table-break" /><p>

  144.    Since data types can be defined in a variety of ways in SQL, and

  145.    <span class="productname">PostgreSQL</span> contains additional ways to

  146.    define data types, their representation in the information schema

  147.    can be somewhat difficult.  The column <code class="literal">data_type</code>

  148.    is supposed to identify the underlying built-in type of the column.

  149.    In <span class="productname">PostgreSQL</span>, this means that the type

  150.    is defined in the system catalog schema

  151.    <code class="literal">pg_catalog</code>.  This column might be useful if the

  152.    application can handle the well-known built-in types specially (for

  153.    example, format the numeric types differently or use the data in

  154.    the precision columns).  The columns <code class="literal">udt_name</code>,

  155.    <code class="literal">udt_schema</code>, and <code class="literal">udt_catalog</code>

  156.    always identify the underlying data type of the column, even if the

  157.    column is based on a domain.  (Since

  158.    <span class="productname">PostgreSQL</span> treats built-in types like

  159.    user-defined types, built-in types appear here as well.  This is an

  160.    extension of the SQL standard.)  These columns should be used if an

  161.    application wants to process data differently according to the

  162.    type, because in that case it wouldn't matter if the column is

  163.    really based on a domain.  If the column is based on a domain, the

  164.    identity of the domain is stored in the columns

  165.    <code class="literal">domain_name</code>, <code class="literal">domain_schema</code>,

  166.    and <code class="literal">domain_catalog</code>.  If you want to pair up

  167.    columns with their associated data types and treat domains as

  168.    separate types, you could write <code class="literal">coalesce(domain_name,

  169.    udt_name)</code>, etc.

  170.   </p></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="infoschema-column-udt-usage.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="information-schema.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="infoschema-constraint-column-usage.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">36.16. <code class="literal">column_udt_usage</code> </td><td width="20%" align="center"><a accesskey="h" href="index.html">Home</a></td><td width="40%" align="right" valign="top"> 36.18. <code class="literal">constraint_column_usage</code></td></tr></table></div></body></html>
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