Provided by: postgresql-client-9.1_9.1.3-2_amd64 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))