pg_type

PostgreSQL 7.3.4 Documentation
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# 3.29. pg_type

This catalog stores information about data types. Scalar types ("base types") are created with `CREATE TYPE`. A complex type is automatically created for each table in the database, to represent the row structure of the table. It is also possible to create complex types with `CREATE TYPE AS`, and derived types with `CREATE DOMAIN`.

Table 3-29. pg_type Columns

Name | Type | References | Description
--- | --- | --- | ---
typname | `name` |  | Data type name
typnamespace | `oid` | pg_namespace.oid | The OID of the namespace that contains this type
typowner | `int4` | pg_shadow.usesysid | Owner (creator) 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. Only `char`, `short`, and `int` equivalent items can be passed by value, so if the type is not 1, 2, or 4 bytes long, PostgreSQL does not have the option of passing by value and so `typbyval` had better be false. Variable-length types are always passed by reference. Note that `typbyval` can be false even if the length would allow pass-by-value; this is currently true for type `float4`, for example.
typtype | `char` |  | `typtype` is b for a base type, c for a complex type (i.e., a table's row type), d for a derived type (i.e., a domain), or p for a pseudo-type. See also `typrelid` and `typbasetype`.
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` | pg_class.oid | If this is a complex type (see `typtype`), then this field 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-complex types.
typelem | `oid` | pg_type.oid | If `typelem` is not 0 then it identifies another row in `pg_type`. The current type can then be subscripted like an array yielding values of type `typelem`. A "true" array type is variable length (`typlen` = -1), but some fixed-length (`typlen` > 0) types also have nonzero `typelem`, for example `name` and `oidvector`. If a fixed-length type has a `typelem` then its internal representation must be N values of the `typelem` data type with no other data. Variable-length array types have a header defined by the array subroutines.
typinput | `regproc` | pg_proc.oid | Input conversion function
typoutput | `regproc` | pg_proc.oid | Output conversion 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). Note: For types used in system tables, it is critical that the size and alignment defined in `pg_type` agree with the way that the compiler will lay out the field in a struct 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': Value must always be stored plain. 'e': Value can be stored in a "secondary" relation (if relation has one, see `pg_class`.`reltoastrelid`). 'm': Value can be stored compressed inline. 'x': Value can be stored compressed inline or in "secondary". Note that 'm' fields can also be moved out to secondary storage, but only as a last resort ('e' and 'x' fields are moved first).
typnotnull | `bool` |  | `typnotnull` represents a NOT NULL constraint on a type. Presently used for domains only.
typbasetype | `oid` | pg_type.oid | If this is a derived type (see `typtype`), then `typbasetype` identifies the type that this one is based on. Zero if not a derived type.
typtypmod | `int4` |  | Domains use `typtypmod` to 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 that is an array (that is, typbasetype is an array type; the domain's typelem will match the base type's typelem). Zero for non-domains and non-array domains.
typdefaultbin | `text` |  | If `typdefaultbin` is not NULL, it is the nodeToString representation of a default expression for the type. Currently 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 may be fed to the type's input converter to produce a constant.

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