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CREATE TYPE()			 SQL Commands			 CREATE TYPE()



NAME
       CREATE TYPE - define a new data type


SYNOPSIS
       CREATE TYPE name AS
	   ( attribute_name data_type [, ... ] )

       CREATE TYPE name (
	   INPUT = input_function,
	   OUTPUT = output_function
	   [ , RECEIVE = receive_function ]
	   [ , SEND = send_function ]
	   [ , ANALYZE = analyze_function ]
	   [ , INTERNALLENGTH = { internallength | VARIABLE } ]
	   [ , PASSEDBYVALUE ]
	   [ , ALIGNMENT = alignment ]
	   [ , STORAGE = storage ]
	   [ , DEFAULT = default ]
	   [ , ELEMENT = element ]
	   [ , DELIMITER = delimiter ]
       )


DESCRIPTION
       CREATE  TYPE registers a new data type for use in the current database.
       The user who defines a type becomes its owner.

       If a schema name is given then the type is  created  in	the  specified
       schema.	Otherwise  it  is created in the current schema. The type name
       must be distinct from the name of any existing type or  domain  in  the
       same  schema. (Because tables have associated data types, the type name
       must also be distinct from the name of any existing table in  the  same
       schema.)

   COMPOSITE TYPES
       The  first form of CREATE TYPE creates a composite type.	 The composite
       type is specified by a list of attribute names and data types.  This is
       essentially  the same as the row type of a table, but using CREATE TYPE
       avoids the need to create an actual table when all that is wanted is to
       define  a type.	A stand-alone composite type is useful as the argument
       or return type of a function.

   BASE TYPES
       The second form of CREATE TYPE creates a new base type  (scalar	type).
       The  parameters	may  appear  in	 any  order, not only that illustrated
       above, and most are optional. You must register two or  more  functions
       (using CREATE FUNCTION) before defining the type. The support functions
       input_function and output_function are required,	 while	the  functions
       receive_function, send_function and analyze_function are optional. Gen-
       erally these functions have to be coded in C or another low-level  lan-
       guage.

       The  input_function converts the type's external textual representation
       to the internal representation used  by	the  operators	and  functions
       defined for the type.  output_function performs the reverse transforma-
       tion. The input function may be declared as taking one argument of type
       cstring,	 or  as taking three arguments of types cstring, oid, integer.
       The first argument is the input text as a C string, the second argument
       is  the	type's	own OID (except for array types, which instead receive
       their element type's OID), and the third is the typmod of the  destina-
       tion  column,  if known (-1 will be passed if not).  The input function
       must return a value of the data type itself.  The output function  must
       be  declared  as	 taking one argument of the new data type.  The output
       function must return type cstring.

       The optional receive_function converts the type's external binary  rep-
       resentation  to	the  internal  representation. If this function is not
       supplied, the type cannot participate in binary input. The binary  rep-
       resentation  should  be chosen to be cheap to convert to internal form,
       while being reasonably portable. (For  example,	the  standard  integer
       data  types  use	 network byte order as the external binary representa-
       tion, while the internal representation is in the machine's native byte
       order.) The receive function should perform adequate checking to ensure
       that the value is valid.	 The receive function may be declared as  tak-
       ing  one	 argument  of  type  internal, or as taking three arguments of
       types internal, oid, integer.  The first argument is  a	pointer	 to  a
       StringInfo  buffer holding the received byte string; the optional argu-
       ments are the same as for the text input function.  The	receive	 func-
       tion  must  return  a  value  of	 the data type itself.	Similarly, the
       optional send_function converts from the internal representation to the
       external	 binary representation.	 If this function is not supplied, the
       type cannot participate in binary output. The  send  function  must  be
       declared	 as  taking one argument of the new data type.	The send func-
       tion must return type bytea.

       You should at this point be wondering how the input  and	 output	 func-
       tions  can  be  declared	 to have results or arguments of the new type,
       when they have to be created before the new type can  be	 created.  The
       answer  is that the input function must be created first, then the out-
       put function (and the binary I/O functions if wanted), and finally  the
       data  type.  PostgreSQL will first see the name of the new data type as
       the return type of the input function. It will create a ''shell'' type,
       which is simply a placeholder entry in the system catalog, and link the
       input function definition to the shell type. Similarly the other	 func-
       tions will be linked to the (now already existing) shell type. Finally,
       CREATE TYPE replaces the shell entry with a complete  type  definition,
       and the new type can be used.

       The optional analyze_function performs type-specific statistics collec-
       tion for columns of the data type.  By default, ANALYZE will attempt to
       gather  statistics using the type's ''equals'' and ''less-than'' opera-
       tors, if there is a default b-tree operator class  for  the  type.  For
       non-scalar types this behavior is likely to be unsuitable, so it can be
       overridden by specifying a custom analysis function. The analysis func-
       tion  must  be declared to take a single argument of type internal, and
       return a boolean	 result.  The  detailed	 API  for  analysis  functions
       appears in src/include/commands/vacuum.h.

       While  the  details  of the new type's internal representation are only
       known to the I/O functions and other functions you create to work  with
       the  type,  there are several properties of the internal representation
       that must be declared to PostgreSQL.  Foremost of  these	 is  internal-
       length.	 Base  data types can be fixed-length, in which case internal-
       length is a positive integer, or variable length, indicated by  setting
       internallength to VARIABLE. (Internally, this is represented by setting
       typlen to -1.) The internal representation of all variable-length types
       must  start with a 4-byte integer giving the total length of this value
       of the type.

       The optional flag PASSEDBYVALUE indicates that values of this data type
       are  passed  by	value,	rather	than by reference. You may not pass by
       value types whose internal representation is larger than	 the  size  of
       the Datum type (4 bytes on most machines, 8 bytes on a few).

       The  alignment  parameter  specifies the storage alignment required for
       the data type. The allowed values equate to alignment on 1, 2, 4, or  8
       byte   boundaries.   Note  that	variable-length	 types	must  have  an
       alignment of at least 4, since they  necessarily	 contain  an  int4  as
       their first component.

       The  storage parameter allows selection of storage strategies for vari-
       able-length data types. (Only plain is allowed for fixed-length types.)
       plain specifies that data of the type will always be stored in-line and
       not compressed.	extended specifies that the system will first  try  to
       compress a long data value, and will move the value out of the main ta-
       ble row if it's still too long.	external allows the value to be	 moved
       out  of	the  main  table,  but the system will not try to compress it.
       main allows compression, but discourages moving the value  out  of  the
       main  table.  (Data items with this storage strategy may still be moved
       out of the main table if there is no other way to make a row  fit,  but
       they  will  be  kept in the main table preferentially over extended and
       external items.)

       A default value may be specified, in case a user wants columns  of  the
       data  type  to default to something other than the null value.  Specify
       the default with the DEFAULT key word.  (Such a default may be overrid-
       den by an explicit DEFAULT clause attached to a particular column.)

       To indicate that a type is an array, specify the type of the array ele-
       ments using the ELEMENT key word. For example, to define	 an  array  of
       4-byte  integers	 (int4),  specify  ELEMENT  = int4. More details about
       array types appear below.

       To indicate the delimiter to be used between  values  in	 the  external
       representation  of  arrays of this type, delimiter can be set to a spe-
       cific character. The default delimiter is the comma (,). Note that  the
       delimiter is associated with the array element type, not the array type
       itself.

   ARRAY TYPES
       Whenever a user-defined base data type is created, PostgreSQL automati-
       cally creates an associated array type, whose name consists of the base
       type's name prepended with an underscore. The parser  understands  this
       naming  convention,  and	 translates requests for columns of type foo[]
       into requests for type _foo.   The  implicitly-created  array  type  is
       variable	 length	 and  uses  the	 built-in  input  and output functions
       array_in and array_out.

       You might reasonably ask why there is an ELEMENT option, if the	system
       makes  the  correct array type automatically.  The only case where it's
       useful to use ELEMENT is when you are making a fixed-length  type  that
       happens	to be internally an array of a number of identical things, and
       you want to allow these things to be accessed directly by subscripting,
       in  addition to whatever operations you plan to provide for the type as
       a whole. For example, type name allows its constituent char elements to
       be  accessed  this way.	A 2-D point type could allow its two component
       numbers to be accessed like point[0]  and  point[1].   Note  that  this
       facility	 only  works  for  fixed-length	 types	whose internal form is
       exactly a sequence of identical fixed-length  fields.  A	 subscriptable
       variable-length	type must have the generalized internal representation
       used by array_in and array_out.	For historical reasons (i.e., this  is
       clearly	wrong  but  it's  far  too late to change it), subscripting of
       fixed-length array types starts from zero, rather than from one as  for
       variable-length arrays.

PARAMETERS
       name   The  name (optionally schema-qualified) of a type to be created.

       attribute_name
	      The name of an attribute (column) for the composite type.

       data_type
	      The name of an existing data type to become a column of the com-
	      posite type.

       input_function
	      The name of a function that converts data from the type's exter-
	      nal textual form to its internal form.

       output_function
	      The name of a function that converts data from the type's inter-
	      nal form to its external textual form.

       receive_function
	      The name of a function that converts data from the type's exter-
	      nal binary form to its internal form.

       send_function
	      The name of a function that converts data from the type's inter-
	      nal form to its external binary form.

       analyze_function
	      The  name	 of  a function that performs statistical analysis for
	      the data type.

       internallength
	      A numeric constant that specifies the length in bytes of the new
	      type's  internal	representation. The default assumption is that
	      it is variable-length.

       alignment
	      The storage alignment requirement of the data  type.  If	speci-
	      fied,  it	 must  be  char, int2, int4, or double; the default is
	      int4.

       storage
	      The storage strategy for the data type. If  specified,  must  be
	      plain, external, extended, or main; the default is plain.

       default
	      The  default  value  for	the data type. If this is omitted, the
	      default is null.

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

       delimiter
	      The delimiter character to be used between values in arrays made
	      of this type.

NOTES
       User-defined type names cannot begin with the underscore character  (_)
       and  can	 only  be  62  characters long (or in general NAMEDATALEN - 2,
       rather than the NAMEDATALEN - 1 characters allowed  for	other  names).
       Type  names  beginning with underscore are reserved for internally-cre-
       ated array type names.

       In PostgreSQL versions before 7.3, it was customary to avoid creating a
       shell  type  by replacing the functions' forward references to the type
       name with the placeholder pseudotype opaque. The cstring arguments  and
       results	also had to be declared as opaque before 7.3. To support load-
       ing of old dump files, CREATE TYPE will accept functions declared using
       opaque,	but  it will issue a notice and change the function's declara-
       tion to use the correct types.

EXAMPLES
       This example creates a composite type and uses it in a function defini-
       tion:

       CREATE TYPE compfoo AS (f1 int, f2 text);

       CREATE FUNCTION getfoo() RETURNS SETOF compfoo AS $$
	   SELECT fooid, fooname FROM foo
       $$ LANGUAGE SQL;


       This example creates the base data type box and then uses the type in a
       table definition:

       CREATE TYPE box (
	   INTERNALLENGTH = 16,
	   INPUT = my_box_in_function,
	   OUTPUT = my_box_out_function
       );

       CREATE TABLE myboxes (
	   id integer,
	   description box
       );


       If the internal structure of box were an array of four float4 elements,
       we might instead use

       CREATE TYPE box (
	   INTERNALLENGTH = 16,
	   INPUT = my_box_in_function,
	   OUTPUT = my_box_out_function,
	   ELEMENT = float4
       );

       which  would  allow  a  box value's component numbers to be accessed by
       subscripting. Otherwise the type behaves the same as before.

       This example creates a large object type and uses it in a table defini-
       tion:

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


       More  examples,	including  suitable input and output functions, are in
       the documentation.

COMPATIBILITY
       This CREATE TYPE command is a PostgreSQL extension. There is  a	CREATE
       TYPE  statement in the SQL standard that is rather different in detail.

SEE ALSO
       CREATE FUNCTION [create_function(7)], DROP TYPE	[drop_type(l)],	 ALTER
       TYPE [alter_type(l)]



SQL - Language Statements	  2010-12-14			 CREATE TYPE()
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