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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 ]
       )

       CREATE TYPE name

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.
       Generally these functions have to be coded in C  or  another  low-level
       language.

       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
       transformation. 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 destination column, if known (-1 will be passed if
       not).  The input function must return a value of the data type  itself.
       Usually,  an input function should be declared STRICT; if it is not, it
       will be called with a NULL first parameter when reading  a  NULL  input
       value.  The  function  must  still  return NULL in this case, unless it
       raises an error.  (This case is mainly meant to  support  domain  input
       functions,  which may need to reject NULL inputs.)  The output function
       must be declared as taking one argument of  the  new  data  type.   The
       output  function  must  return  type cstring.  Output functions are not
       invoked for NULL values.

       The optional  receive_function  converts  the  type’s  external  binary
       representation  to the internal representation. If this function is not
       supplied, the type cannot  participate  in  binary  input.  The  binary
       representation  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
       representation, 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 taking 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 arguments are the same as for the text  input  function.   The
       receive function must return a value of the data type itself.  Usually,
       a receive function should be declared STRICT; if it is not, it will  be
       called with a NULL first parameter when reading a NULL input value. The
       function must still return NULL in  this  case,  unless  it  raises  an
       error.  (This case is mainly meant to support domain receive functions,
       which may  need  to  reject  NULL  inputs.)   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  function  must
       return type bytea.  Send functions are not invoked for NULL values.

       You  should  at  this  point  be  wondering  how  the  input and output
       functions 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 type should first be defined as a shell type,  which
       is  a  placeholder  type  that  has  no properties except a name and an
       owner. This is done by issuing the command CREATE TYPE  name,  with  no
       additional   parameters.   Then   the  I/O  functions  can  be  defined
       referencing the shell type. Finally, CREATE TYPE with a full definition
       replaces  the shell entry with a complete, valid type definition, after
       which the new type can be used normally.

       The  optional  analyze_function   performs   type-specific   statistics
       collection  for  columns  of  the  data type.  By default, ANALYZE will
       attempt to gather statistics using the type’s  ‘‘equals’’  and  ‘‘less-
       than’’  operators,  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 function 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
       internallength.  Base data types can be  fixed-length,  in  which  case
       internallength  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
       variable-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 table 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
       overridden by an explicit  DEFAULT  clause  attached  to  a  particular
       column.)

       To  indicate  that  a  type  is an array, specify the type of the array
       elements 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
       specific 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
       automatically  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
              composite type.

       input_function
              The  name  of  a  function  that  converts  data from the type’s
              external textual form to its internal form.

       output_function
              The name of a  function  that  converts  data  from  the  type’s
              internal form to its external textual form.

       receive_function
              The  name  of  a  function  that  converts  data from the type’s
              external binary form to its internal form.

       send_function
              The name of a  function  that  converts  data  from  the  type’s
              internal 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
              specified,  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-
       created array type names.

       Because there are no restrictions on use of a data type once it’s  been
       created,  creating a base type is tantamount to granting public execute
       permission on the functions mentioned  in  the  type  definition.  (The
       creator of the type is therefore required to own these functions.) This
       is usually not an issue for the sorts of functions that are useful in a
       type  definition.  But you might want to think twice before designing a
       type in a way that would require  ‘‘secret’’  information  to  be  used
       while converting it to or from external form.

       Before  PostgreSQL  version  8.2,  the  syntax CREATE TYPE name did not
       exist.  The way to create a new base  type  was  to  create  its  input
       function  first.   In this approach, PostgreSQL will first see the name
       of the new data type as the return type of  the  input  function.   The
       shell  type is implicitly created in this situation, and then it can be
       referenced in the definitions of the  remaining  I/O  functions.   This
       approach  still  works, but is deprecated and may be disallowed in some
       future release. Also, to avoid  accidentally  cluttering  the  catalogs
       with shell types as a result of simple typos in function definitions, a
       shell type will only be made  this  way  when  the  input  function  is
       written in C.

       In PostgreSQL versions before 7.3, it was customary to avoid creating a
       shell type at all, 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  loading  of  old  dump  files,  CREATE  TYPE  will  accept I/O
       functions declared using opaque, but it will issue a notice and  change
       the function declarations to use the correct types.

EXAMPLES

       This  example  creates  a  composite  type  and  uses  it in a function
       definition:

       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;

       CREATE FUNCTION my_box_in_function(cstring) RETURNS box AS ... ;
       CREATE FUNCTION my_box_out_function(box) RETURNS cstring AS ... ;

       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
       definition:

       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 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)], CREATE DOMAIN [create_domain(l)]