Man Pages

create_type(7) - phpMan create_type(7) - phpMan

Command: man perldoc info search(apropos)  


CREATE TYPE(7)                   SQL Commands                   CREATE TYPE(7)



NAME
       CREATE TYPE - define a new data type


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

       CREATE TYPE name AS ENUM
           ( 'label' [, ... ] )

       CREATE TYPE name (
           INPUT = input_function,
           OUTPUT = output_function
           [ , RECEIVE = receive_function ]
           [ , SEND = send_function ]
           [ , TYPMOD_IN = type_modifier_input_function ]
           [ , TYPMOD_OUT = type_modifier_output_function ]
           [ , ANALYZE = analyze_function ]
           [ , INTERNALLENGTH = { internallength | VARIABLE } ]
           [ , PASSEDBYVALUE ]
           [ , ALIGNMENT = alignment ]
           [ , STORAGE = storage ]
           [ , LIKE = like_type ]
           [ , CATEGORY = category ]
           [ , PREFERRED = preferred ]
           [ , 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 cur-
       rent  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.

   ENUMERATED TYPES
       The second form of CREATE TYPE creates an enumerated (enum) type, as described in in the  documentation.   Enum
       types take a list of one or more quoted labels, each of which must be less than NAMEDATALEN bytes long (64 in a
       standard PostgreSQL build).

   BASE TYPES
       The third form of CREATE TYPE creates a new base type (scalar type). To create a new base type, you must  be  a
       superuser.   (This  restriction  is  made  because an erroneous type definition could confuse or even crash the
       server.)

       The parameters can appear in any order, not only that illustrated above, and most are optional. You must regis-
       ter  two  or more functions (using CREATE FUNCTION) before defining the type. The support functions input_func-
       tion   and   output_function   are   required,   while   the   functions    receive_function,    send_function,
       type_modifier_input_function,  type_modifier_output_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 can 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 might 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  representa-
       tion.  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 can 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 might need to reject NULL inputs.)  Similarly, the optional send_func-
       tion 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 argu-
       ment 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  type_modifier_input_function  and  type_modifier_output_function are needed if the type supports
       modifiers, that is optional constraints attached to a type declaration, such as char(5) or numeric(30,2). Post-
       greSQL  allows  user-defined  types  to take one or more simple constants or identifiers as modifiers. However,
       this information must be capable of being packed into a single non-negative integer value for  storage  in  the
       system  catalogs.  The type_modifier_input_function is passed the declared modifier(s) in the form of a cstring
       array. It must check the values for validity (throwing an error if they are wrong), and if  they  are  correct,
       return  a  single non-negative integer value that will be stored as the column ''typmod''.  Type modifiers will
       be rejected if the type does not have a type_modifier_input_function.  The  type_modifier_output_function  con-
       verts  the  internal  integer  typmod value back to the correct form for user display. It must return a cstring
       value that is the exact string to append to the type name; for example numeric's function might return  (30,2).
       It  is  allowed to omit the type_modifier_output_function, in which case the default display format is just the
       stored typmod integer value enclosed in parentheses.

       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 func-
       tions 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  cannot  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 might 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.)

       The  like_type parameter provides an alternative method for specifying the basic representation properties of a
       data type: copy them from some existing type. The values of internallength, passedbyvalue, alignment, and stor-
       age are copied from the named type. (It is possible, though usually undesirable, to override some of these val-
       ues by specifying them along with the LIKE clause.) Specifying representation this  way  is  especially  useful
       when the low-level implementation of the new type ''piggybacks'' on an existing type in some fashion.

       The  category  and  preferred  parameters  can  be  used to help control which implicit cast will be applied in
       ambiguous situations. Each data type belongs to a category named by a single ASCII character, and each type  is
       either  ''preferred''  or  not within its category. The parser will prefer casting to preferred types (but only
       from other types within the same category) when this rule is helpful in resolving overloaded functions or oper-
       ators.  For  more  details see in the documentation. For types that have no implicit casts to or from any other
       types, it is sufficient to leave these settings at the defaults.  However, for a group of  related  types  that
       have  implicit  casts, it is often helpful to mark them all as belonging to a category and select one or two of
       the ''most general'' types as being preferred within the category.  The category parameter is especially useful
       when adding a user-defined type to an existing built-in category, such as the numeric or string types. However,
       it is also possible to create new entirely-user-defined type categories. Select any ASCII character other  than
       an upper-case letter to name such a category.

       A  default  value can 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 can 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 type is created, PostgreSQL automatically creates an associated array type, whose name
       consists of the base type's name prepended with an underscore, and truncated if necessary to keep it less  than
       NAMEDATALEN  bytes long. (If the name so generated collides with an existing type name, the process is repeated
       until a non-colliding name is found.)  This implicitly-created array type  is  variable  length  and  uses  the
       built-in  input  and  output functions array_in and array_out. The array type tracks any changes in its element
       type's owner or schema, and is dropped if the element type is.

       You might reasonably ask why there is an ELEMENT option, if the system makes the correct array  type  automati-
       cally.   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 point is represented as just two floating-point numbers,  which  it  allows  to  be  accessed  as
       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  gener-
       alized  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.

       label  A string literal representing the textual label associated with one value of an enum 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.

       type_modifier_input_function
              The name of a function that converts an array of modifier(s) for the type into internal form.

       type_modifier_output_function
              The  name  of  a  function that converts the internal form of the type's modifier(s) to external textual
              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 dou-
              ble; 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.

       like_type
              The  name of an existing data type that the new type will have the same representation as. The values of
              internallength, passedbyvalue, alignment, and storage are copied from that type,  unless  overridden  by
              explicit specification elsewhere in this CREATE TYPE command.

       category
              The  category  code  (a  single  ASCII  character) for this type.  The default is 'U' for ''user-defined
              type''.  Other standard category codes can be found in in the documentation. You may also  choose  other
              ASCII characters in order to create custom categories.

       preferred
              True  if  this  type  is a preferred type within its type category, else false. The default is false. Be
              very careful about creating a new preferred type within an existing type category, as this  could  cause
              surprising changes in behavior.

       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
       Because  there are no restrictions on use of a data type once it's been created, creating a base type is tanta-
       mount to granting public execute permission on the functions mentioned in the type definition.  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  8.3, the name of a generated array type was always exactly the element type's name
       with one underscore character (_) prepended. (Type names were therefore restricted in length to one less  char-
       acter  than other names.)  While this is still usually the case, the array type name may vary from this in case
       of maximum-length names or collisions with user type names  that  begin  with  underscore.  Writing  code  that
       depends  on  this  convention  is  therefore deprecated. Instead, use pg_type.typarray to locate the array type
       associated with a given type.

       It may be advisable to avoid using type and table names that begin  with  underscore.  While  the  server  will
       change  generated array type names to avoid collisions with user-given names, there is still risk of confusion,
       particularly with old client software that may assume that type names beginning with underscores always  repre-
       sent arrays.

       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 might 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  declara-
       tions 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 an enumerated type and uses it in a table definition:

       CREATE TYPE bug_status AS ENUM ('new', 'open', 'closed');

       CREATE TABLE bug (
           id serial,
           description text,
           status bug_status
       );


       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(7)], ALTER TYPE [alter_type(7)], CREATE DOMAIN [cre-
       ate_domain(7)]



SQL - Language Statements         2014-02-17                    CREATE TYPE(7)