Provided by: postgresql-client-9.1_9.1.3-2_i386 bug

NAME

       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 (
           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 ]
           [ , 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.)

   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.

   Enumerated Types
       The second form of CREATE TYPE creates an enumerated (enum) type, as
       described in Section 8.7, "Enumerated Types", 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 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 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 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 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.

       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 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 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, Type
       Conversion, 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.

       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 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 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 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 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.

       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 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 45.49, "typcategory Codes". 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 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
       less 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 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 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 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
       Section 35.11, "User-defined Types", in the documentation.

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 CREATE
       TABLE).

SEE ALSO

       ALTER TYPE (ALTER_TYPE(7)), CREATE DOMAIN (CREATE_DOMAIN(7)), CREATE
       FUNCTION (CREATE_FUNCTION(7)), DROP TYPE (DROP_TYPE(7))