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CREATE TYPE

Name

CREATE TYPE — Defines a new base data type
CREATE TYPE typename (
        INPUT          = input_function
      , OUTPUT         = output_function
      , INTERNALLENGTH = (internallength | VARIABLE)
    [ , EXTERNALLENGTH = (externallength | VARIABLE) ]
    [ , ELEMENT        = element ]
    [ , DELIMITER      = delimiter ]
    [ , DEFAULT        = "default" ]
    [ , SEND           = send_function ]
    [ , RECEIVE        = receive_function ]
    [ , PASSEDBYVALUE ]
)
  

Inputs

typename

The name of a type to be created.

INTERNALLENGTH internallength

A literal value, which specifies the internal length of the new type.

EXTERNALLENGTH externallength

A literal value, which specifies the external length of the new type.

INPUT input_function

The name of a function, created by CREATE FUNCTION, which converts data from its external form to the type's internal form.

OUTPUT output_function

The name of a function, created by CREATE FUNCTION, which converts data from its internal form to a form suitable for display.

element

The type being created is an array; this specifies the type of the array elements.

delimiter

The delimiter character for the array.

default

The default text to be displayed to indicate "data not present"

send_function

The name of a function, created by CREATE FUNCTION, which converts data of this type into a form suitable for transmission to another machine.

receive_function

The name of a function, created by CREATE FUNCTION, which converts data of this type from a form suitable for transmission from another machine to internal form.

Outputs

CREATE

Message returned if the type is successfully created.

Description

CREATE TYPE allows the user to register a new user data type with Postgres for use in the current data base. The user who defines a type becomes its owner. typename is the name of the new type and must be unique within the types defined for this database.

CREATE TYPE requires the registration of two functions (using create function) before defining the type. The representation of a new base type is determined by input_function, which converts the type's external representation to an internal representation usable by the operators and functions defined for the type. Naturally, output_function performs the reverse transformation. Both the input and output functions must be declared to take one or two arguments of type "opaque".

New base data types can be fixed length, in which case internallength is a positive integer, or variable length, in which case Postgres assumes that the new type has the same format as the Postgres-supplied data type, "text". To indicate that a type is variable-length, set internallength to VARIABLE. The external representation is similarly specified using the externallength keyword.

To indicate that a type is an array and to indicate that a type has array elements, indicate the type of the array element using the element keyword. For example, to define an array of 4 byte integers ("int4"), specify

ELEMENT = int4

To indicate the delimiter to be used on arrays of this type, delimiter can be set to a specific character. The default delimiter is the comma (",").

A default value is optionally available in case a user wants some specific bit pattern to mean "data not present." Specify the default with the DEFAULT keyword.

The optional functions send_function and receive_function are used when the application program requesting Postgres services resides on a different machine. In this case, the machine on which Postgres runs may use a format for the data type different from that used on the remote machine. In this case it is appropriate to convert data items to a standard form when sending from the server to the client and converting from the standard format to the machine specific format when the server receives the data from the client. If these functions are not specified, then it is assumed that the internal format of the type is acceptable on all relevant machine architectures. For example, single characters do not have to be converted if passed from a Sun-4 to a DECstation, but many other types do.

The optional flag, PASSEDBYVALUE, indicates that operators and functions which use this data type should be passed an argument by value rather than by reference. Note that you may not pass by value types whose internal representation is more than four bytes.

For new base types, a user can define operators, functions and aggregates using the appropriate facilities described in this section.

Array Types

Two generalized built-in functions, array_in and array_out, exist for quick creation of variable-length array types. These functions operate on arrays of any existing Postgres type.

Large Object Types

A "regular" Postgres type can only be 8192 bytes in length. If you need a larger type you must create a Large Object type. The interface for these types is discussed at length in The PostgreSQL Programmer's Guide. The length of all large object types is always VARIABLE.

Examples

This command creates the box data type and then uses the type in a class definition:

CREATE TYPE box (INTERNALLENGTH = 8,
    INPUT = my_procedure_1, OUTPUT = my_procedure_2);
CREATE TABLE myboxes (id INT4, description box);
  

This command creates a variable length array type with integer elements.

CREATE TYPE int4array (INPUT = array_in, OUTPUT = array_out,
    INTERNALLENGTH = VARIABLE, ELEMENT = int4);
CREATE TABLE myarrays (id int4, numbers int4array);
   

This command creates a large object type and uses it in a class definition:

CREATE TYPE bigobj (INPUT = lo_filein, OUTPUT = lo_fileout,
    INTERNALLENGTH = VARIABLE);
CREATE TABLE big_objs (id int4, obj bigobj);
   

Restrictions

Type names cannot begin with the underscore character ("_") and can only be 31 characters long. This is because Postgres silently creates an array type for each base type with a name consisting of the base type's name prepended with an underscore.

Notes

Refer to DROP TYPE to remove an existing type.

See also CREATE FUNCTION, CREATE OPERATOR and the chapter on Large Objects in the PostgreSQL Programmer's Guide.

Compatibility

SQL3

CREATE TYPE is an SQL3 statement.

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