PostgreSQL

37.16. `columns`
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37.16. `columns`

The view columns contains information about all table columns (or view columns) in the database. System columns (oid, 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).

Table 37.14. columns Columns

Name Data Type Description

Name	Data Type	Description
`table_catalog`	`sql_identifier`	Name of the database containing the table (always the current database)
`table_schema`	`sql_identifier`	Name of the schema containing the table
`table_name`	`sql_identifier`	Name of the table
`column_name`	`sql_identifier`	Name of the column
`ordinal_position`	`cardinal_number`	Ordinal position of the column within the table (count starts at 1)
`column_default`	`character_data`	Default expression of the column
`is_nullable`	`yes_or_no`	`YES` if the column is possibly nullable, `NO` 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.
`data_type`	`character_data`	Data type of the column, if it is a built-in type, or `ARRAY` if it is some array (in that case, see the view `element_types`), else `USER-DEFINED` (in that case, the type is identified in `udt_name` 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 `domain_name` and associated columns).
`character_maximum_length`	`cardinal_number`	If `data_type` identifies a character or bit string type, the declared maximum length; null for all other data types or if no maximum length was declared.
`character_octet_length`	`cardinal_number`	If `data_type` 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.
`numeric_precision`	`cardinal_number`	If `data_type` 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 `numeric_precision_radix`. For all other data types, this column is null.
`numeric_precision_radix`	`cardinal_number`	If `data_type` identifies a numeric type, this column indicates in which base the values in the columns `numeric_precision` and `numeric_scale` are expressed. The value is either 2 or 10. For all other data types, this column is null.
`numeric_scale`	`cardinal_number`	If `data_type` 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 `numeric_precision_radix`. For all other data types, this column is null.
`datetime_precision`	`cardinal_number`	If `data_type` 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.
`interval_type`	`character_data`	If `data_type` identifies an interval type, this column contains the specification which fields the intervals include for this column, e.g., `YEAR TO MONTH`, `DAY TO SECOND`, etc. If no field restrictions were specified (that is, the interval accepts all fields), and for all other data types, this field is null.
`interval_precision`	`cardinal_number`	Applies to a feature not available in PostgreSQL (see `datetime_precision` for the fractional seconds precision of interval type columns)
`character_set_catalog`	`sql_identifier`	Applies to a feature not available in PostgreSQL
`character_set_schema`	`sql_identifier`	Applies to a feature not available in PostgreSQL
`character_set_name`	`sql_identifier`	Applies to a feature not available in PostgreSQL
`collation_catalog`	`sql_identifier`	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
`collation_schema`	`sql_identifier`	Name of the schema containing the collation of the column, null if default or the data type of the column is not collatable
`collation_name`	`sql_identifier`	Name of the collation of the column, null if default or the data type of the column is not collatable
`domain_catalog`	`sql_identifier`	If the column has a domain type, the name of the database that the domain is defined in (always the current database), else null.
`domain_schema`	`sql_identifier`	If the column has a domain type, the name of the schema that the domain is defined in, else null.
`domain_name`	`sql_identifier`	If the column has a domain type, the name of the domain, else null.
`udt_catalog`	`sql_identifier`	Name of the database that the column data type (the underlying type of the domain, if applicable) is defined in (always the current database)
`udt_schema`	`sql_identifier`	Name of the schema that the column data type (the underlying type of the domain, if applicable) is defined in
`udt_name`	`sql_identifier`	Name of the column data type (the underlying type of the domain, if applicable)
`scope_catalog`	`sql_identifier`	Applies to a feature not available in PostgreSQL
`scope_schema`	`sql_identifier`	Applies to a feature not available in PostgreSQL
`scope_name`	`sql_identifier`	Applies to a feature not available in PostgreSQL
`maximum_cardinality`	`cardinal_number`	Always null, because arrays always have unlimited maximum cardinality in PostgreSQL
`dtd_identifier`	`sql_identifier`	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.)
`is_self_referencing`	`yes_or_no`	Applies to a feature not available in PostgreSQL
`is_identity`	`yes_or_no`	If the column is an identity column, then `YES`, else `NO`.
`identity_generation`	`character_data`	If the column is an identity column, then `ALWAYS` or `BY DEFAULT`, reflecting the definition of the column.
`identity_start`	`character_data`	If the column is an identity column, then the start value of the internal sequence, else null.
`identity_increment`	`character_data`	If the column is an identity column, then the increment of the internal sequence, else null.
`identity_maximum`	`character_data`	If the column is an identity column, then the maximum value of the internal sequence, else null.
`identity_minimum`	`character_data`	If the column is an identity column, then the minimum value of the internal sequence, else null.
`identity_cycle`	`yes_or_no`	If the column is an identity column, then `YES` if the internal sequence cycles or `NO` if it does not; otherwise null.
`is_generated`	`character_data`	Applies to a feature not available in PostgreSQL
`generation_expression`	`character_data`	Applies to a feature not available in PostgreSQL
`is_updatable`	`yes_or_no`	`YES` if the column is updatable, `NO` if not (Columns in base tables are always updatable, columns in views not necessarily)

table_catalog

sql_identifier

Name of the database containing the table (always the current database)

table_schema

sql_identifier

Name of the schema containing the table

table_name

sql_identifier

Name of the table

column_name

sql_identifier

Name of the column

ordinal_position

cardinal_number

Ordinal position of the column within the table (count starts at 1)

column_default

character_data

Default expression of the column

is_nullable

yes_or_no

YES if the column is possibly nullable, NO 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.

data_type

character_data

Data type of the column, if it is a built-in type, or ARRAY if it is some array (in that case, see the view element_types), else USER-DEFINED (in that case, the type is identified in udt_name 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 domain_name and associated columns).

character_maximum_length

cardinal_number

If data_type identifies a character or bit string type, the declared maximum length; null for all other data types or if no maximum length was declared.

character_octet_length

cardinal_number

If data_type 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.

numeric_precision

cardinal_number

If data_type 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 numeric_precision_radix. For all other data types, this column is null.

numeric_precision_radix

cardinal_number

If data_type identifies a numeric type, this column indicates in which base the values in the columns numeric_precision and numeric_scale are expressed. The value is either 2 or 10. For all other data types, this column is null.

numeric_scale

cardinal_number

If data_type 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 numeric_precision_radix. For all other data types, this column is null.

datetime_precision

cardinal_number

If data_type 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.

interval_type

character_data

If data_type identifies an interval type, this column contains the specification which fields the intervals include for this column, e.g., YEAR TO MONTH, DAY TO SECOND, etc. If no field restrictions were specified (that is, the interval accepts all fields), and for all other data types, this field is null.

interval_precision

cardinal_number

Applies to a feature not available in PostgreSQL (see datetime_precision for the fractional seconds precision of interval type columns)

character_set_catalog

sql_identifier

Applies to a feature not available in PostgreSQL

character_set_schema

sql_identifier

Applies to a feature not available in PostgreSQL

character_set_name

sql_identifier

Applies to a feature not available in PostgreSQL

collation_catalog

sql_identifier

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

collation_schema

sql_identifier

Name of the schema containing the collation of the column, null if default or the data type of the column is not collatable

collation_name

sql_identifier

Name of the collation of the column, null if default or the data type of the column is not collatable

domain_catalog

sql_identifier

If the column has a domain type, the name of the database that the domain is defined in (always the current database), else null.

domain_schema

sql_identifier

If the column has a domain type, the name of the schema that the domain is defined in, else null.

domain_name

sql_identifier

If the column has a domain type, the name of the domain, else null.

udt_catalog

sql_identifier

Name of the database that the column data type (the underlying type of the domain, if applicable) is defined in (always the current database)

udt_schema

sql_identifier

Name of the schema that the column data type (the underlying type of the domain, if applicable) is defined in

udt_name

sql_identifier

Name of the column data type (the underlying type of the domain, if applicable)

scope_catalog

sql_identifier

Applies to a feature not available in PostgreSQL

scope_schema

sql_identifier

Applies to a feature not available in PostgreSQL

scope_name

sql_identifier

Applies to a feature not available in PostgreSQL

maximum_cardinality

cardinal_number

Always null, because arrays always have unlimited maximum cardinality in PostgreSQL

dtd_identifier

sql_identifier

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.)

is_self_referencing

yes_or_no

Applies to a feature not available in PostgreSQL

is_identity

yes_or_no

If the column is an identity column, then YES, else NO.

identity_generation

character_data

If the column is an identity column, then ALWAYS or BY DEFAULT, reflecting the definition of the column.

identity_start

character_data

If the column is an identity column, then the start value of the internal sequence, else null.

identity_increment

character_data

If the column is an identity column, then the increment of the internal sequence, else null.

identity_maximum

character_data

If the column is an identity column, then the maximum value of the internal sequence, else null.

identity_minimum

character_data

If the column is an identity column, then the minimum value of the internal sequence, else null.

identity_cycle

yes_or_no

If the column is an identity column, then YES if the internal sequence cycles or NO if it does not; otherwise null.

is_generated

character_data

Applies to a feature not available in PostgreSQL

generation_expression

character_data

Applies to a feature not available in PostgreSQL

is_updatable

yes_or_no

YES if the column is updatable, NO if not (Columns in base tables are always updatable, columns in views not necessarily)

Since data types can be defined in a variety of ways in SQL, and PostgreSQL contains additional ways to define data types, their representation in the information schema can be somewhat difficult. The column data_type is supposed to identify the underlying built-in type of the column. In PostgreSQL, this means that the type is defined in the system catalog schema pg_catalog. 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 udt_name, udt_schema, and udt_catalog always identify the underlying data type of the column, even if the column is based on a domain. (Since PostgreSQL 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 domain_name, domain_schema, and domain_catalog. If you want to pair up columns with their associated data types and treat domains as separate types, you could write coalesce(domain_name, udt_name), etc.

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37.15. column_udt_usage

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37.17. constraint_column_usage

PostgreSQL

37.16. columns

37.16. `columns`