pg_type — PostgreSQL system catalog

The PostgreSQL pg_type system catalog: full column reference (names, types, descriptions), catalog relationships and version support.

The Sev-1 Admin
The Sev-1 Admin  ·  7 min read

Summary

The catalog pg_type stores information about data types. Base types and enum types (scalar types) are created with CREATE TYPE, and domains with CREATE DOMAIN. A composite type is automatically created for each table in the database, to represent the row structure of the table. It is also possible to create composite types with CREATE TYPE AS.

(Description quoted from the official PostgreSQL documentation.)

Columns

The pg_type system catalog exposes the following columns (names, types and descriptions are taken verbatim from the PostgreSQL documentation):

  • oid oid
    Row identifier
  • typname name
    Data type name
  • typnamespace oid references pg_namespace.oid
    The OID of the namespace that contains this type
  • typowner oid references pg_authid.oid
    Owner of the type
  • typlen int2
    For a fixed-size type, typlen is the number of bytes in the internal representation of the type. But for a variable-length type, typlen is negative. -1 indicates a “varlena” type (one that has a length word), -2 indicates a null-terminated C string.
  • typbyval bool
    typbyval determines whether internal routines pass a value of this type by value or by reference. typbyval had better be false if typlen is not 1, 2, or 4 (or 8 on machines where Datum is 8 bytes). Variable-length types are always passed by reference. Note that typbyval can be false even if the length would allow pass-by-value.
  • typtype char
    typtype is b for a base type, c for a composite type (e.g., a table’s row type), d for a domain, e for an enum type, p for a pseudo-type, r for a range type, or m for a multirange type. See also typrelid and typbasetype.
  • typcategory char
    typcategory is an arbitrary classification of data types that is used by the parser to determine which implicit casts should be “preferred”. See typcategory_table.
  • typispreferred bool
    True if the type is a preferred cast target within its typcategory
  • typisdefined bool
    True if the type is defined, false if this is a placeholder entry for a not-yet-defined type. When typisdefined is false, nothing except the type name, namespace, and OID can be relied on.
  • typdelim char
    Character that separates two values of this type when parsing array input. Note that the delimiter is associated with the array element data type, not the array data type.
  • typrelid oid references pg_class.oid
    If this is a composite type (see typtype), then this column points to the pg_class entry that defines the corresponding table. (For a free-standing composite type, the pg_class entry doesn’t really represent a table, but it is needed anyway for the type’s pg_attribute entries to link to.) Zero for non-composite types.
  • typsubscript regproc references pg_proc.oid
    Subscripting handler function’s OID, or zero if this type doesn’t support subscripting. Types that are “true” array types have typsubscript = array_subscript_handler, but other types may have other handler functions to implement specialized subscripting behavior.
  • typelem oid references pg_type.oid
    If typelem is not zero then it identifies another row in pg_type, defining the type yielded by subscripting. This should be zero if typsubscript is zero. However, it can be zero when typsubscript isn’t zero, if the handler doesn’t need typelem to determine the subscripting result type. Note that a typelem dependency is considered to imply physical containment of the element type in this type; so DDL changes on the element type might be restricted by the presence of this type.
  • typarray oid references pg_type.oid
    If typarray is not zero then it identifies another row in pg_type, which is the “true” array type having this type as element
  • typinput regproc references pg_proc.oid
    Input conversion function (text format)
  • typoutput regproc references pg_proc.oid
    Output conversion function (text format)
  • typreceive regproc references pg_proc.oid
    Input conversion function (binary format), or zero if none
  • typsend regproc references pg_proc.oid
    Output conversion function (binary format), or zero if none
  • typmodin regproc references pg_proc.oid
    Type modifier input function, or zero if type does not support modifiers
  • typmodout regproc references pg_proc.oid
    Type modifier output function, or zero to use the standard format
  • typanalyze regproc references pg_proc.oid
    Custom analyze function, or zero to use the standard function
  • typalign char
    typalign is the alignment required when storing a value of this type. It applies to storage on disk as well as most representations of the value inside PostgreSQL. When multiple values are stored consecutively, such as in the representation of a complete row on disk, padding is inserted before a datum of this type so that it begins on the specified boundary. The alignment reference is the beginning of the first datum in the sequence. Possible values are: c = char alignment, i.e., no alignment needed. s = short alignment (2 bytes on most machines). i = int alignment (4 bytes on most machines). d = double alignment (8 bytes on many machines, but by no means all).
  • typstorage char
    typstorage tells for varlena types (those with typlen = -1) if the type is prepared for toasting and what the default strategy for attributes of this type should be. Possible values are: p (plain): Values must always be stored plain (non-varlena types always use this value). e (external): Values can be stored in a secondary “TOAST” relation (if relation has one, see pg_class.reltoastrelid). m (main): Values can be compressed and stored inline. x (extended): Values can be compressed and/or moved to a secondary relation.
  • typnotnull bool
    typnotnull represents a not-null constraint on a type. Used for domains only.
  • typbasetype oid references pg_type.oid
    If this is a domain (see typtype), then typbasetype identifies the type that this one is based on. Zero if this type is not a domain.
  • typtypmod int4
    Domains use typtypmod to tuple/">record the typmod to be applied to their base type (-1 if base type does not use a typmod). -1 if this type is not a domain.
  • typndims int4
    typndims is the number of array dimensions for a domain over an array (that is, typbasetype is an array type). Zero for types other than domains over array types.
  • typcollation oid references pg_collation.oid
    typcollation specifies the collation of the type. If the type does not support collations, this will be zero. A base type that supports collations will have a nonzero value here, typically DEFAULT_COLLATION_OID. A domain over a collatable type can have a collation OID different from its base type’s, if one was specified for the domain.
  • typdefaultbin pg_node_tree
    If typdefaultbin is not null, it is the nodeToString() representation of a default expression for the type. This is only used for domains.
  • typdefault text
    typdefault is null if the type has no associated default value. If typdefaultbin is not null, typdefault must contain a human-readable version of the default expression represented by typdefaultbin. If typdefaultbin is null and typdefault is not, then typdefault is the external representation of the type’s default value, which can be fed to the type’s input converter to produce a constant.
  • typacl aclitem[]
    Access privileges; see ddl_priv for details

Related catalogs

This object references the following other system catalogs:

Version applicability

Present in PostgreSQL 17, 18, 19 (verified against each release’s documentation). This is a long-standing system object that also exists in earlier PostgreSQL releases.

Related & references

Reference: PostgreSQL documentation — pg_type.