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><A
NAME="INFOSCHEMA-COLUMNS"
>34.16. <TT
CLASS="LITERAL"
>columns</TT
></A
></H1
><P
>   The view <TT
CLASS="LITERAL"
>columns</TT
> contains information about all
   table columns (or view columns) in the database.  System columns
   (<TT
CLASS="LITERAL"
>oid</TT
>, etc.) are not included.  Only those columns are
   shown that the current user has access to (by way of being the
   owner or having some privilege).
  </P
><DIV
CLASS="TABLE"
><A
NAME="AEN48342"
></A
><P
><B
>Table 34-14. <TT
CLASS="LITERAL"
>columns</TT
> Columns</B
></P
><TABLE
BORDER="1"
CLASS="CALSTABLE"
><COL><COL><COL><THEAD
><TR
><TH
>Name</TH
><TH
>Data Type</TH
><TH
>Description</TH
></TR
></THEAD
><TBODY
><TR
><TD
><TT
CLASS="LITERAL"
>table_catalog</TT
></TD
><TD
><TT
CLASS="TYPE"
>sql_identifier</TT
></TD
><TD
>Name of the database containing the table (always the current database)</TD
></TR
><TR
><TD
><TT
CLASS="LITERAL"
>table_schema</TT
></TD
><TD
><TT
CLASS="TYPE"
>sql_identifier</TT
></TD
><TD
>Name of the schema containing the table</TD
></TR
><TR
><TD
><TT
CLASS="LITERAL"
>table_name</TT
></TD
><TD
><TT
CLASS="TYPE"
>sql_identifier</TT
></TD
><TD
>Name of the table</TD
></TR
><TR
><TD
><TT
CLASS="LITERAL"
>column_name</TT
></TD
><TD
><TT
CLASS="TYPE"
>sql_identifier</TT
></TD
><TD
>Name of the column</TD
></TR
><TR
><TD
><TT
CLASS="LITERAL"
>ordinal_position</TT
></TD
><TD
><TT
CLASS="TYPE"
>cardinal_number</TT
></TD
><TD
>Ordinal position of the column within the table (count starts at 1)</TD
></TR
><TR
><TD
><TT
CLASS="LITERAL"
>column_default</TT
></TD
><TD
><TT
CLASS="TYPE"
>character_data</TT
></TD
><TD
>Default expression of the column</TD
></TR
><TR
><TD
><TT
CLASS="LITERAL"
>is_nullable</TT
></TD
><TD
><TT
CLASS="TYPE"
>yes_or_no</TT
></TD
><TD
>       <TT
CLASS="LITERAL"
>YES</TT
> if the column is possibly nullable,
       <TT
CLASS="LITERAL"
>NO</TT
> if it is known not nullable.  A not-null
       constraint is one way a column can be known not nullable, but
       there can be others.
      </TD
></TR
><TR
><TD
><TT
CLASS="LITERAL"
>data_type</TT
></TD
><TD
><TT
CLASS="TYPE"
>character_data</TT
></TD
><TD
>       Data type of the column, if it is a built-in type, or
       <TT
CLASS="LITERAL"
>ARRAY</TT
> if it is some array (in that case, see
       the view <TT
CLASS="LITERAL"
>element_types</TT
>), else
       <TT
CLASS="LITERAL"
>USER-DEFINED</TT
> (in that case, the type is
       identified in <TT
CLASS="LITERAL"
>udt_name</TT
> and associated
       columns).  If the column is based on a domain, this column
       refers to the type underlying the domain (and the domain is
       identified in <TT
CLASS="LITERAL"
>domain_name</TT
> and associated
       columns).
      </TD
></TR
><TR
><TD
><TT
CLASS="LITERAL"
>character_maximum_length</TT
></TD
><TD
><TT
CLASS="TYPE"
>cardinal_number</TT
></TD
><TD
>       If <TT
CLASS="LITERAL"
>data_type</TT
> identifies a character or bit
       string type, the declared maximum length; null for all other
       data types or if no maximum length was declared.
      </TD
></TR
><TR
><TD
><TT
CLASS="LITERAL"
>character_octet_length</TT
></TD
><TD
><TT
CLASS="TYPE"
>cardinal_number</TT
></TD
><TD
>       If <TT
CLASS="LITERAL"
>data_type</TT
> identifies a character type,
       the maximum possible length in octets (bytes) of a datum; null
       for all other data types.  The maximum octet length depends on
       the declared character maximum length (see above) and the
       server encoding.
      </TD
></TR
><TR
><TD
><TT
CLASS="LITERAL"
>numeric_precision</TT
></TD
><TD
><TT
CLASS="TYPE"
>cardinal_number</TT
></TD
><TD
>       If <TT
CLASS="LITERAL"
>data_type</TT
> identifies a numeric type, this
       column contains the (declared or implicit) precision of the
       type for this column.  The precision indicates the number of
       significant digits.  It can be expressed in decimal (base 10)
       or binary (base 2) terms, as specified in the column
       <TT
CLASS="LITERAL"
>numeric_precision_radix</TT
>.  For all other data
       types, this column is null.
      </TD
></TR
><TR
><TD
><TT
CLASS="LITERAL"
>numeric_precision_radix</TT
></TD
><TD
><TT
CLASS="TYPE"
>cardinal_number</TT
></TD
><TD
>       If <TT
CLASS="LITERAL"
>data_type</TT
> identifies a numeric type, this
       column indicates in which base the values in the columns
       <TT
CLASS="LITERAL"
>numeric_precision</TT
> and
       <TT
CLASS="LITERAL"
>numeric_scale</TT
> are expressed.  The value is
       either 2 or 10.  For all other data types, this column is null.
      </TD
></TR
><TR
><TD
><TT
CLASS="LITERAL"
>numeric_scale</TT
></TD
><TD
><TT
CLASS="TYPE"
>cardinal_number</TT
></TD
><TD
>       If <TT
CLASS="LITERAL"
>data_type</TT
> identifies an exact numeric
       type, this column contains the (declared or implicit) scale of
       the type for this column.  The scale indicates the number of
       significant digits to the right of the decimal point.  It can
       be expressed in decimal (base 10) or binary (base 2) terms, as
       specified in the column
       <TT
CLASS="LITERAL"
>numeric_precision_radix</TT
>.  For all other data
       types, this column is null.
      </TD
></TR
><TR
><TD
><TT
CLASS="LITERAL"
>datetime_precision</TT
></TD
><TD
><TT
CLASS="TYPE"
>cardinal_number</TT
></TD
><TD
>       If <TT
CLASS="LITERAL"
>data_type</TT
> identifies a date, time,
       timestamp, or interval type, this column contains the (declared
       or implicit) fractional seconds precision of the type for this
       column, that is, the number of decimal digits maintained
       following the decimal point in the seconds value.  For all
       other data types, this column is null.
      </TD
></TR
><TR
><TD
><TT
CLASS="LITERAL"
>interval_type</TT
></TD
><TD
><TT
CLASS="TYPE"
>character_data</TT
></TD
><TD
>       If <TT
CLASS="LITERAL"
>data_type</TT
> identifies an interval type,
       this column contains the specification which fields the
       intervals include for this column, e.g., <TT
CLASS="LITERAL"
>YEAR TO
       MONTH</TT
>, <TT
CLASS="LITERAL"
>DAY TO SECOND</TT
>, etc.  If no
       field restrictions were specified (that is, the interval
       accepts all fields), and for all other data types, this field
       is null.
      </TD
></TR
><TR
><TD
><TT
CLASS="LITERAL"
>interval_precision</TT
></TD
><TD
><TT
CLASS="TYPE"
>cardinal_number</TT
></TD
><TD
>       Applies to a feature not available
       in <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
>
       (see <TT
CLASS="LITERAL"
>datetime_precision</TT
> for the fractional
       seconds precision of interval type columns)
      </TD
></TR
><TR
><TD
><TT
CLASS="LITERAL"
>character_set_catalog</TT
></TD
><TD
><TT
CLASS="TYPE"
>sql_identifier</TT
></TD
><TD
>Applies to a feature not available in <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
></TD
></TR
><TR
><TD
><TT
CLASS="LITERAL"
>character_set_schema</TT
></TD
><TD
><TT
CLASS="TYPE"
>sql_identifier</TT
></TD
><TD
>Applies to a feature not available in <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
></TD
></TR
><TR
><TD
><TT
CLASS="LITERAL"
>character_set_name</TT
></TD
><TD
><TT
CLASS="TYPE"
>sql_identifier</TT
></TD
><TD
>Applies to a feature not available in <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
></TD
></TR
><TR
><TD
><TT
CLASS="LITERAL"
>collation_catalog</TT
></TD
><TD
><TT
CLASS="TYPE"
>sql_identifier</TT
></TD
><TD
>       Name of the database containing the collation of the column
       (always the current database), null if default or the data type
       of the column is not collatable
      </TD
></TR
><TR
><TD
><TT
CLASS="LITERAL"
>collation_schema</TT
></TD
><TD
><TT
CLASS="TYPE"
>sql_identifier</TT
></TD
><TD
>       Name of the schema containing the collation of the column, null
       if default or the data type of the column is not collatable
      </TD
></TR
><TR
><TD
><TT
CLASS="LITERAL"
>collation_name</TT
></TD
><TD
><TT
CLASS="TYPE"
>sql_identifier</TT
></TD
><TD
>       Name of the collation of the column, null if default or the
       data type of the column is not collatable
      </TD
></TR
><TR
><TD
><TT
CLASS="LITERAL"
>domain_catalog</TT
></TD
><TD
><TT
CLASS="TYPE"
>sql_identifier</TT
></TD
><TD
>       If the column has a domain type, the name of the database that
       the domain is defined in (always the current database), else
       null.
      </TD
></TR
><TR
><TD
><TT
CLASS="LITERAL"
>domain_schema</TT
></TD
><TD
><TT
CLASS="TYPE"
>sql_identifier</TT
></TD
><TD
>       If the column has a domain type, the name of the schema that
       the domain is defined in, else null.
      </TD
></TR
><TR
><TD
><TT
CLASS="LITERAL"
>domain_name</TT
></TD
><TD
><TT
CLASS="TYPE"
>sql_identifier</TT
></TD
><TD
>If the column has a domain type, the name of the domain, else null.</TD
></TR
><TR
><TD
><TT
CLASS="LITERAL"
>udt_catalog</TT
></TD
><TD
><TT
CLASS="TYPE"
>sql_identifier</TT
></TD
><TD
>       Name of the database that the column data type (the underlying
       type of the domain, if applicable) is defined in (always the
       current database)
      </TD
></TR
><TR
><TD
><TT
CLASS="LITERAL"
>udt_schema</TT
></TD
><TD
><TT
CLASS="TYPE"
>sql_identifier</TT
></TD
><TD
>       Name of the schema that the column data type (the underlying
       type of the domain, if applicable) is defined in
      </TD
></TR
><TR
><TD
><TT
CLASS="LITERAL"
>udt_name</TT
></TD
><TD
><TT
CLASS="TYPE"
>sql_identifier</TT
></TD
><TD
>       Name of the column data type (the underlying type of the
       domain, if applicable)
      </TD
></TR
><TR
><TD
><TT
CLASS="LITERAL"
>scope_catalog</TT
></TD
><TD
><TT
CLASS="TYPE"
>sql_identifier</TT
></TD
><TD
>Applies to a feature not available in <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
></TD
></TR
><TR
><TD
><TT
CLASS="LITERAL"
>scope_schema</TT
></TD
><TD
><TT
CLASS="TYPE"
>sql_identifier</TT
></TD
><TD
>Applies to a feature not available in <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
></TD
></TR
><TR
><TD
><TT
CLASS="LITERAL"
>scope_name</TT
></TD
><TD
><TT
CLASS="TYPE"
>sql_identifier</TT
></TD
><TD
>Applies to a feature not available in <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
></TD
></TR
><TR
><TD
><TT
CLASS="LITERAL"
>maximum_cardinality</TT
></TD
><TD
><TT
CLASS="TYPE"
>cardinal_number</TT
></TD
><TD
>Always null, because arrays always have unlimited maximum cardinality in <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
></TD
></TR
><TR
><TD
><TT
CLASS="LITERAL"
>dtd_identifier</TT
></TD
><TD
><TT
CLASS="TYPE"
>sql_identifier</TT
></TD
><TD
>       An identifier of the data type descriptor of the column, unique
       among the data type descriptors pertaining to the table.  This
       is mainly useful for joining with other instances of such
       identifiers.  (The specific format of the identifier is not
       defined and not guaranteed to remain the same in future
       versions.)
      </TD
></TR
><TR
><TD
><TT
CLASS="LITERAL"
>is_self_referencing</TT
></TD
><TD
><TT
CLASS="TYPE"
>yes_or_no</TT
></TD
><TD
>Applies to a feature not available in <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
></TD
></TR
><TR
><TD
><TT
CLASS="LITERAL"
>is_identity</TT
></TD
><TD
><TT
CLASS="TYPE"
>yes_or_no</TT
></TD
><TD
>Applies to a feature not available in <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
></TD
></TR
><TR
><TD
><TT
CLASS="LITERAL"
>identity_generation</TT
></TD
><TD
><TT
CLASS="TYPE"
>character_data</TT
></TD
><TD
>Applies to a feature not available in <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
></TD
></TR
><TR
><TD
><TT
CLASS="LITERAL"
>identity_start</TT
></TD
><TD
><TT
CLASS="TYPE"
>character_data</TT
></TD
><TD
>Applies to a feature not available in <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
></TD
></TR
><TR
><TD
><TT
CLASS="LITERAL"
>identity_increment</TT
></TD
><TD
><TT
CLASS="TYPE"
>character_data</TT
></TD
><TD
>Applies to a feature not available in <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
></TD
></TR
><TR
><TD
><TT
CLASS="LITERAL"
>identity_maximum</TT
></TD
><TD
><TT
CLASS="TYPE"
>character_data</TT
></TD
><TD
>Applies to a feature not available in <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
></TD
></TR
><TR
><TD
><TT
CLASS="LITERAL"
>identity_minimum</TT
></TD
><TD
><TT
CLASS="TYPE"
>character_data</TT
></TD
><TD
>Applies to a feature not available in <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
></TD
></TR
><TR
><TD
><TT
CLASS="LITERAL"
>identity_cycle</TT
></TD
><TD
><TT
CLASS="TYPE"
>yes_or_no</TT
></TD
><TD
>Applies to a feature not available in <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
></TD
></TR
><TR
><TD
><TT
CLASS="LITERAL"
>is_generated</TT
></TD
><TD
><TT
CLASS="TYPE"
>character_data</TT
></TD
><TD
>Applies to a feature not available in <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
></TD
></TR
><TR
><TD
><TT
CLASS="LITERAL"
>generation_expression</TT
></TD
><TD
><TT
CLASS="TYPE"
>character_data</TT
></TD
><TD
>Applies to a feature not available in <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
></TD
></TR
><TR
><TD
><TT
CLASS="LITERAL"
>is_updatable</TT
></TD
><TD
><TT
CLASS="TYPE"
>yes_or_no</TT
></TD
><TD
>       <TT
CLASS="LITERAL"
>YES</TT
> if the column is updatable,
       <TT
CLASS="LITERAL"
>NO</TT
> if not (Columns in base tables are always
       updatable, columns in views not necessarily)
      </TD
></TR
></TBODY
></TABLE
></DIV
><P
>   Since data types can be defined in a variety of ways in SQL, and
   <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> contains additional ways to
   define data types, their representation in the information schema
   can be somewhat difficult.  The column <TT
CLASS="LITERAL"
>data_type</TT
>
   is supposed to identify the underlying built-in type of the column.
   In <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
>, this means that the type
   is defined in the system catalog schema
   <TT
CLASS="LITERAL"
>pg_catalog</TT
>.  This column might be useful if the
   application can handle the well-known built-in types specially (for
   example, format the numeric types differently or use the data in
   the precision columns).  The columns <TT
CLASS="LITERAL"
>udt_name</TT
>,
   <TT
CLASS="LITERAL"
>udt_schema</TT
>, and <TT
CLASS="LITERAL"
>udt_catalog</TT
>
   always identify the underlying data type of the column, even if the
   column is based on a domain.  (Since
   <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> treats built-in types like
   user-defined types, built-in types appear here as well.  This is an
   extension of the SQL standard.)  These columns should be used if an
   application wants to process data differently according to the
   type, because in that case it wouldn't matter if the column is
   really based on a domain.  If the column is based on a domain, the
   identity of the domain is stored in the columns
   <TT
CLASS="LITERAL"
>domain_name</TT
>, <TT
CLASS="LITERAL"
>domain_schema</TT
>,
   and <TT
CLASS="LITERAL"
>domain_catalog</TT
>.  If you want to pair up
   columns with their associated data types and treat domains as
   separate types, you could write <TT
CLASS="LITERAL"
>coalesce(domain_name,
   udt_name)</TT
>, etc.
  </P
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