The catalog pg_type stores information about data types. Base 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.
Table 43-34. pg_type Columns
|Data type name
|The OID of the namespace that contains this type
|Owner of the type
|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 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; this is currently true for type float4, for example
|typtype is b for a base type, c for a composite type (e.g., a table's row type), d for a domain, or p for a pseudo-type. See also typrelid and typbasetype
|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
|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
|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
|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 point. If a fixed-length type has a typelem then its internal representation must be some number of values of the typelem data type with no other data. Variable-length array types have a header defined by the array subroutines
|Input conversion function (text format)
|Output conversion function (text format)
|Input conversion function (binary format), or 0 if none
|Output conversion function (binary format), or 0 if none
|Custom ANALYZE function, or 0 to use the standard function
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:
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
Note that m columns can also be moved out to secondary storage, but only as a last resort (e and x columns are moved first).
typnotnull represents a not-null constraint on a type. Used for domains only
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
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 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 types other than array domains
If typdefaultbin is not null, it is the
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