CREATE TYPE

Function

CREATE TYPE defines a new data type in the current database. The user who defines a new data type becomes its owner. Types are designed only for row-store tables.

Four types of data can be created by using CREATE TYPE: composite data, base data, a shell data, and enumerated data.

Precautions

If a schema name is given, the type will be created in the specified schema. Otherwise, it will be 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.)

Syntax

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

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

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

Parameter Description

Composite types

Base types

When creating a base type, you can place parameters in any order. The input_function and output_function parameters are mandatory, and other parameters are optional.

Whenever a user-defined type is created, GaussDB(DWS) automatically creates an associated array type whose name consists of the element type name prepended with an underscore (_).

Example

Example 1: Create a composite type, create a table, insert data, and make a query.

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CREATE TYPE compfoo AS (f1 int, f2 text);
CREATE TABLE t1_compfoo(a int, b compfoo);
CREATE TABLE t2_compfoo(a int, b compfoo);
INSERT INTO t1_compfoo values(1,(1,'demo'));
INSERT INTO t2_compfoo select * from t1_compfoo;
SELECT (b).f1 FROM t1_compfoo;
SELECT * FROM t1_compfoo t1 join t2_compfoo t2 on (t1.b).f1=(t1.b).f1;

Example 2: Create an enumeration type and use it in the table definition.

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CREATE TYPE bugstatus AS ENUM ('create', 'modify', 'closed');
CREATE TABLE customer (name text,current_bugstatus bugstatus);
INSERT INTO customer VALUES ('type','create');
SELECT * FROM customer WHERE current_bugstatus = 'create';

Example 3: Compile a .so file and create the shell type.

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CREATE TYPE complex;

This statement creates a placeholder for the type to be created, which can then be referenced when defining its I/O functions. Now you can define an I/O function. Note that the function must be declared in NOT FENCED mode when it is created.

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CREATE FUNCTION
complex_in(cstring)
    RETURNS complex
    AS 'filename'
    LANGUAGE C IMMUTABLE STRICT not fenced;

CREATE FUNCTION
complex_out(complex)
    RETURNS cstring
    AS 'filename'
    LANGUAGE C IMMUTABLE STRICT not fenced;

CREATE FUNCTION
complex_recv(internal)
    RETURNS complex
    AS 'filename'
    LANGUAGE C IMMUTABLE STRICT not fenced;

CREATE FUNCTION
complex_send(complex)
    RETURNS bytea
    AS 'filename'
    LANGUAGE C IMMUTABLE STRICT not fenced;

-- Finally, provide a complete definition of the data type:

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CREATE TYPE complex (
internallength = 16,
input = complex_in,
output = complex_out,
receive = complex_recv,
send = complex_send,
alignment = double
);

The C functions corresponding to the input, output, receive, and send functions are defined as follows:

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-- Define a structure body Complex:
typedef struct Complex {
    double      x;
    double      y;
} Complex;

-- Define an input function:
PG_FUNCTION_INFO_V1(complex_in);

Datum
complex_in(PG_FUNCTION_ARGS)
{
    char       *str = PG_GETARG_CSTRING(0);
    double      x,
                y;
    Complex    *result;

    if (sscanf(str, " ( %lf , %lf )", &x, &y) != 2)
        ereport(ERROR,
                (errcode(ERRCODE_INVALID_TEXT_REPRESENTATION),
                 errmsg("invalid input syntax for complex: \"%s\"",
                        str)));

    result = (Complex *) palloc(sizeof(Complex));
    result->x = x;
    result->y = y;
    PG_RETURN_POINTER(result);
}

-- Define an output function:
PG_FUNCTION_INFO_V1(complex_out);

Datum
complex_out(PG_FUNCTION_ARGS)
{
        Complex    *complex = (Complex *) PG_GETARG_POINTER(0);
        char       *result;

        result = (char *) palloc(100);
        snprintf(result, 100, "(%g,%g)", complex->x, complex->y);
        PG_RETURN_CSTRING(result);
}

-- Define a receive function:
PG_FUNCTION_INFO_V1(complex_recv);

Datum
complex_recv(PG_FUNCTION_ARGS)
{
    StringInfo  buf = (StringInfo) PG_GETARG_POINTER(0);
    Complex    *result;

    result = (Complex *) palloc(sizeof(Complex));
    result->x = pq_getmsgfloat8(buf);
    result->y = pq_getmsgfloat8(buf);
    PG_RETURN_POINTER(result);
}

-- Define a send function:
PG_FUNCTION_INFO_V1(complex_send);

Datum
complex_send(PG_FUNCTION_ARGS)
{
    Complex    *complex = (Complex *) PG_GETARG_POINTER(0);
    StringInfoData buf;

    pq_begintypsend(&buf);
    pq_sendfloat8(&buf, complex->x);
    pq_sendfloat8(&buf, complex->y);
    PG_RETURN_BYTEA_P(pq_endtypsend(&buf));
}

Helpful Links

ALTER TYPE, DROP TYPE

Parent topic: DDL Syntax