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CREATE TYPE

   CREATE TYPE — define a new data type

Synopsis

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

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

CREATE TYPE name AS RANGE (
    SUBTYPE = subtype
    [ , SUBTYPE_OPCLASS = subtype_operator_class ]
    [ , COLLATION = collation ]
    [ , CANONICAL = canonical_function ]
    [ , SUBTYPE_DIFF = subtype_diff_function ]
    [ , MULTIRANGE_TYPE_NAME = multirange_type_name ]
)

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 ]
    [ , SUBSCRIPT = subscript_function ]
    [ , INTERNALLENGTH = { internallength | VARIABLE } ]
    [ , PASSEDBYVALUE ]
    [ , ALIGNMENT = alignment ]
    [ , STORAGE = storage ]
    [ , LIKE = like_type ]
    [ , CATEGORY = category ]
    [ , PREFERRED = preferred ]
    [ , DEFAULT = default ]
    [ , ELEMENT = element ]
    [ , DELIMITER = delimiter ]
    [ , COLLATABLE = collatable ]
)

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.)

   There are five forms of CREATE TYPE, as shown in the syntax synopsis
   above. They respectively create a composite type, an enum type, a range
   type, a base type, or a shell type. The first four of these are
   discussed in turn below. A shell type is simply a placeholder for a
   type to be defined later; it is created by issuing CREATE TYPE with no
   parameters except for the type name. Shell types are needed as forward
   references when creating range types and base types, as discussed in
   those sections.

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. An
   attribute's collation can be specified too, if its data type is
   collatable. A composite type 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, for example, as the argument or return type
   of a function.

   To be able to create a composite type, you must have USAGE privilege on
   all attribute types.

Enumerated Types

   The second form of CREATE TYPE creates an enumerated (enum) type, as
   described in Section 8.7. Enum types take a list of quoted labels, each
   of which must be less than NAMEDATALEN bytes long (64 bytes in a
   standard PostgreSQL build). (It is possible to create an enumerated
   type with zero labels, but such a type cannot be used to hold values
   before at least one label is added using ALTER TYPE.)

Range Types

   The third form of CREATE TYPE creates a new range type, as described in
   Section 8.17.

   The range type's subtype can be any type with an associated b-tree
   operator class (to determine the ordering of values for the range
   type). Normally the subtype's default b-tree operator class is used to
   determine ordering; to use a non-default operator class, specify its
   name with subtype_opclass. If the subtype is collatable, and you want
   to use a non-default collation in the range's ordering, specify the
   desired collation with the collation option.

   The optional canonical function must take one argument of the range
   type being defined, and return a value of the same type. This is used
   to convert range values to a canonical form, when applicable. See
   Section 8.17.8 for more information. Creating a canonical function is a
   bit tricky, since it must be defined before the range type can be
   declared. To do this, you must first create 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 function can be declared using the
   shell type as argument and result, and finally the range type can be
   declared using the same name. This automatically replaces the shell
   type entry with a valid range type.

   The optional subtype_diff function must take two values of the subtype
   type as argument, and return a double precision value representing the
   difference between the two given values. While this is optional,
   providing it allows much greater efficiency of GiST indexes on columns
   of the range type. See Section 8.17.8 for more information.

   The optional multirange_type_name parameter specifies the name of the
   corresponding multirange type. If not specified, this name is chosen
   automatically as follows. If the range type name contains the substring
   range, then the multirange type name is formed by replacement of the
   range substring with multirange in the range type name. Otherwise, the
   multirange type name is formed by appending a _multirange suffix to the
   range type name.

Base Types

   The fourth 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 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, type_modifier_input_function,
   type_modifier_output_function, analyze_function, and subscript_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 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 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_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 C 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). PostgreSQL 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
   converts 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.

   The optional subscript_function allows the data type to be subscripted
   in SQL commands. Specifying this function does not cause the type to be
   considered a “true” array type; for example, it will not be a candidate
   for the result type of ARRAY[] constructs. But if subscripting a value
   of the type is a natural notation for extracting data from it, then a
   subscript_function can be written to define what that means. The
   subscript function must be declared to take a single argument of type
   internal, and return an internal result, which is a pointer to a struct
   of methods (functions) that implement subscripting. The detailed API
   for subscript functions appears in src/include/nodes/subscripting.h. It
   may also be useful to read the array implementation in
   src/backend/utils/adt/arraysubs.c, or the simpler code in
   contrib/hstore/hstore_subs.c. Additional information appears in Array
   Types below.

   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. (Note that the length field is often
   encoded, as described in Section 66.2; it's unwise to access it
   directly.)

   The optional flag PASSEDBYVALUE indicates that values of this data type
   are passed by value, rather than by reference. Types passed by value
   must be fixed-length, and their internal representation cannot be
   larger than the size of the Datum type (4 bytes on some machines, 8
   bytes on others).

   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.)

   All storage values other than plain imply that the functions of the
   data type can handle values that have been toasted, as described in
   Section 66.2 and Section 36.13.1. The specific other value given merely
   determines the default TOAST storage strategy for columns of a
   toastable data type; users can pick other strategies for individual
   columns using ALTER TABLE SET STORAGE.

   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 storage are copied from the named type. (It is possible, though
   usually undesirable, to override some of these values 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 operators. For more details see Chapter 10. 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 a fixed-length array type, 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. For
   more details, see Array Types 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.

   If the optional Boolean parameter collatable is true, column
   definitions and expressions of the type may carry collation information
   through use of the COLLATE clause. It is up to the implementations of
   the functions operating on the type to actually make use of the
   collation information; this does not happen automatically merely by
   marking the type collatable.

Array Types

   Whenever a user-defined type is created, PostgreSQL automatically
   creates an associated array type, whose name consists of the element
   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. Furthermore, this type is what the system uses
   for constructs such as ARRAY[] over the user-defined type. 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 automatically. The main 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 can be accessed using 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. 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.

   Specifying the SUBSCRIPT option allows a data type to be subscripted,
   even though the system does not otherwise regard it as an array type.
   The behavior just described for fixed-length arrays is actually
   implemented by the SUBSCRIPT handler function
   raw_array_subscript_handler, which is used automatically if you specify
   ELEMENT for a fixed-length type without also writing SUBSCRIPT.

   When specifying a custom SUBSCRIPT function, it is not necessary to
   specify ELEMENT unless the SUBSCRIPT handler function needs to consult
   typelem to find out what to return. Be aware that specifying ELEMENT
   causes the system to assume that the new type contains, or is somehow
   physically dependent on, the element type; thus for example changing
   properties of the element type won't be allowed if there are any
   columns of the dependent type.

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.

   collation
          The name of an existing collation to be associated with a column
          of a composite type, or with a range type.

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

   subtype
          The name of the element type that the range type will represent
          ranges of.

   subtype_operator_class
          The name of a b-tree operator class for the subtype.

   canonical_function
          The name of the canonicalization function for the range type.

   subtype_diff_function
          The name of a difference function for the subtype.

   multirange_type_name
          The name of the corresponding multirange 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.

   subscript_function
          The name of a function that defines what subscripting a value of
          the data type does.

   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.

   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 Table 52.65. 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.

   collatable
          True if this type's operations can use collation information.
          The default is false.

Notes

   Because there are no restrictions on use of a data type once it's been
   created, creating a base type or range type is tantamount 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
   fewer character 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 represent arrays.

   Before PostgreSQL version 8.2, the shell-type creation 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 version 16 and later, it is desirable for base types'
   input functions to return “soft” errors using the new
   errsave()/ereturn() mechanism, rather than throwing ereport()
   exceptions as in previous versions. See src/backend/utils/fmgr/README
   for more information.

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 a range type:
CREATE TYPE float8_range AS RANGE (subtype = float8, subtype_diff = float8mi);

   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
   Section 36.13.

Compatibility

   The first form of the CREATE TYPE command, which creates a composite
   type, conforms to the SQL standard. The other forms are PostgreSQL
   extensions. The CREATE TYPE statement in the SQL standard also defines
   other forms that are not implemented in PostgreSQL.

   The ability to create a composite type with zero attributes is a
   PostgreSQL-specific deviation from the standard (analogous to the same
   case in CREATE TABLE).

See Also

   ALTER TYPE, CREATE DOMAIN, CREATE FUNCTION, DROP TYPE