GNU/Linux man pages
Livre :
Expressions régulières,
Syntaxe et mise en oeuvre :
GNU/Linux |
RedHat 5.2(Apollo) |
|
 |
create_type(l) |
 |
create type - define a new base data type
create type typename (internallength = (number | variable),
|
[ externallength = (number | variable), ] | ||
|
input = input_function, | ||
|
output = output_function | ||
|
[, element = typename] | ||
|
[, delimiter = <character>] | ||
|
[, default = "string" ] | ||
|
[, send = send_function ] | ||
|
[, receive = receive_function ] | ||
|
[, passedbyvalue]) |
Create type allows the user to register a new user data type with Postgres for use in the current data base. The user who defines a type becomes its owner. Typename is the name of the new type and must be unique within the types defined for this database.
Create type requires the registration of two functions (using create function(l)) before defining the type. The representation of a new base type is determined by input_function, which converts the type’s external representation to an internal representation usable by the operators and functions defined for the type. Naturally, output_function performs the reverse transformation. Both the input and output functions must be declared to take one or two arguments of type “opaque”.
New base data types can be fixed length, in which case internallength is a positive integer, or variable length, in which case Postgres assumes that the new type has the same format as the Postgres-supplied data type, “text”. To indicate that a type is variable-length, set internallength to variable. The external representation is similarly specified using the externallength keyword.
To indicate
that a type is an array and to indicate that a type has
array elements, indicate the type of the array element using
the element keyword. For example, to define an array
of 4 byte integers (“int4”), specify
element = int4
To indicate the delimiter to be used on arrays of this type, delimiter can be set to a specific character. The default delimiter is the comma (“,”) character.
A default value is optionally available in case a user wants some specific bit pattern to mean “data not present.”
The optional functions send_function and receive_function are used when the application program requesting Postgres services resides on a different machine. In this case, the machine on which Postgres runs may use a different format for the data type than used on the remote machine. In this case it is appropriate to convert data items to a standard form when sending from the server to the client and converting from the standard format to the machine specific format when the server receives the data from the client. If these functions are not specified, then it is assumed that the internal format of the type is acceptable on all relevant machine architectures. For example, single characters do not have to be converted if passed from a Sun-4 to a DECstation, but many other types do.
The optional passedbyvalue flag indicates that operators and functions which use this data type should be passed an argument by value rather than by reference. Note that only types whose internal representation is at most four bytes may be passed by value.
For new base types, a user can define operators, functions and aggregates using the appropriate facilities described in this section.
Two generalized built-in functions, array_in and array_out, exist for quick creation of variable-length array types. These functions operate on arrays of any existing Postgres type.
A “regular” Postgres type can only be 8192 bytes in length. If you need a larger type you must create a Large Object type. The interface for these types is discussed at length in Section 7, the large object interface. The length of all large object types is always variable, meaning the internallength for large objects is always -1.
--
--This command creates the box data type and then uses the
--type in a class definition
--
create type box (internallength = 8,
|
input = my_procedure_1, output = my_procedure_2) |
create table
MYBOXES (id = int4, description = box)
--
--This command creates a variable length array type with
--integer elements.
--
create type int4array
(input = array_in, output = array_out,
internallength = variable, element = int4)
create table
MYARRAYS (id = int4, numbers = int4array)
--
--This command creates a large object type and uses it in
--a class definition.
--
create type bigobj
(input = lo_filein, output = lo_fileout,
internallength = variable)
create table BIG_OBJS (id = int4, obj = bigobj)
Type names cannot begin with the underscore character (“_”) and can only be 15 characters long. This is because Postgres silently creates an array type for each base type with a name consisting of the base type’s name prepended with an underscore.
create function(l), create operator(l), drop type(l), large_objects(3).
|
create_type(l) | |