Help Center/ GaussDB/ Developer Guide(Distributed_2.x)/ System Catalogs and System Views/ System Catalogs/ PG_TYPE
Updated on 2024-10-14 GMT+08:00
View PDF
Share

PG_TYPE

PG_TYPE stores information about data types.

Table 1 PG_TYPE columns

Name

Type

Description

oid

oid

Row identifier (hidden attribute, which must be specified)

typname

name

Data type name

typnamespace

oid

OID of the namespace that contains the type

typowner

oid

Owner of the type

typlen

smallint
Number of bytes in the internal representation of the type for a fixed-size type. It is a negative number for a variable-length type.
  • The value -1 indicates a "varlena" type (one that has a length word).
  • The value -2 indicates a null-terminated C string.

typbyval

boolean

Specifies whether to pass a value (true) or a reference (false) when a value of this type is passed internally. typbyval is false if the type of typlen is not 1, 2, 4, or 8, because values of this type are always passed by reference of this column. typbyval can be false even if the typlen is passed by a parameter of this column.

typtype

"char"
  • b: base type.
  • c: composite type (for example, a table's row type)
  • d: domain
  • p: pseudo
  • r: range
  • e: enumeration
  • o: set type

For details, see typrelid and typbasetype.

typcategory

"char"

Fuzzy classification of data types, which can be used by parsers as the basis for data conversion.

typispreferred

boolean

The value is true if conversion is performed when data meets conversion rules specified by typcategory. Otherwise, the conversion is not performed.

typisdefined

boolean

Whether a type has been defined. It is true if the type is defined, and false if this is a placeholder entry for a not-yet-defined type. When it 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 an array input. Note that the delimiter is associated with the array element data type, not the array data type.

typrelid

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 does not represent a table, but it is required for the type's PG_ATTRIBUTE entries to link to. It is 0 for non-composite type.

typelem

oid

If typelem is not 0, it identifies another row in PG_TYPE. The current type can be described as an array yielding values of type typelem. A "true" array type has a variable length (typlen = -1), but some fixed-length types (typlen > 0) also have non-zero typelem, for example name and point. If a fixed-length type has a typelem, its internal representation must be a number of values of the typelem data type with no other data. Variable-length array types have a header defined by the array subroutines.

typarray

oid

If the value is not 0, the corresponding type record is available in PG_TYPE.

typinput

regproc

Input conversion function (text format)

typoutput

regproc

Output conversion function (text format)

typreceive

regproc

Input conversion function (binary format); 0 for non-input conversion function

typsend

regproc

Output conversion function (binary format); 0 for non-output conversion function

typmodin

regproc

Type modifier input function; 0 if the type does not support modifiers

typmodout

regproc

Type modifier output function; 0 if the type does not support modifiers

typanalyze

regproc

Custom ANALYZE function; 0 if the standard function is used

typalign

"char"
Alignment required when storing a value of this type. It applies to storage on disks as well as most representations of the value. When multiple values are stored consecutively, such as in the representation of a complete row on disk, padding is inserted before a data 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, that is, no alignment needed
  • s: short alignment (2 bytes on most machines)
  • i: integer alignment (4 bytes on most machines)
  • d: double alignment (8 bytes on many machines, but by no means all)
NOTICE:

For types used in system tables, the size and alignment defined in PG_TYPE must agree with the way that the compiler lays out the column in a structure representing a table row.

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: Values are always stored plain.
  • e: Value can be stored in a secondary relationship (if the relation has one, see pg_class.reltoastrelid).
  • m: Values can be stored compressed inline.
  • x: Values can be stored compressed inline or stored in secondary storage.
NOTICE:

m domains can also be moved out to secondary storage, but only as a last resort (e and x domains are moved first).

typnotnull

boolean

Whether the type has a NOTNULL constraint. Currently, it is used for domains only.

typbasetype

oid

If this is a domain (see typtype), then typbasetype identifies the type that this one is based on. The value is 0 if this type is not a derived type.

typtypmod

integer

Records the typtypmod to be applied to domains' base types by domains (the value is –1 if the base type does not use typmod). This is –1 if this type is not a domain.

typndims

integer

Number of array dimensions for a domain that is an array (typbasetype is an array type; the domain's typelem matches the base type's typelem). This is 0 for types other than domains over array types.

typcollation

oid

Sorting rule of a specified type. For details about the values, see the PG_COLLATION system catalog. (0 if sequencing is not supported)

typdefaultbin

pg_node_tree

nodeToString() representation of a default expression for the type if the value is non-null. Currently, this column is only used for domains.

typdefault

text

The value is NULL if a type has no associated default value. If typdefaultbin is not set to NULL, typdefault must contain a 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 permission
Parent topic: System Catalogs