User-defined Subtypes

In PL/SQL, SUBTYPE can be used to create its own subtypes. The base type can be any basic type or user-defined type. Subtypes can provide data type compatibility, display the intended use of data items of that type, and detect values that are out of range.

The basic definition syntax of SUBTYPE is as follows:

SUBTYPE subtype_name IS base_type  [ { ( precision [, scale ] ) | RANGE low_value .. high_value } ] [ NOT NULL ]

Parameters:

• SUBTYPE: SUBTYPE keyword.
• subtype_name: name of the subtype to be defined.
• base_type: base type, which can be the base type or user-defined type based on which the subtype is created.
• precision [, scale ]: typmod constraints that can be added.
• RANGE low_value .. high_value: range constraints that can be added.
• NOT NULL: NOT NULL constraints that can be added.

• base_type supports basic types, user-defined data types, and subtypes.
• If the typmod constraint is specified, when a value is assigned to a variable of the SUBTYPE type, the system checks whether the value complies with the typmod constraint and whether the specified typmod constraint can be consistent with the base type.
• Range constraints can be specified only for the int types, including TINYINT, SMALLINT, MEDIUMINT, INTEGER, BINARY_INTEGER, BIGINT, and INT. If the range constraints are specified, the system checks whether the value is within the specified range when assigning a value to a subtype variable.
• The upper and lower limits of RANGE cannot exceed INT64.
• Currently, the RANGE constraints cannot be used when a variable is created.
• The constraint status is updated when the SUBTYPE type is nested or a variable of the SUBTYPE type is created.
• If NOT NULL is specified, variables of the SUBTYPE type must be initialized and cannot be assigned NULL values.
• The SUBTYPE type can be used as the input and output parameter types of stored procedures.
• Subtype variables can be specified using %type and %rowtype. %type supports all base types, and %rowtype supports tables but does not support sets.
• Subtypes support base type constructors.
• The specified character set is not supported.
• This command can be used only in A-compatible database.
• If a database is upgraded from a version that does not support subtypes to a version that supports subtypes and the upgrade is not committed, subtypes cannot be used.

Example 1: An unconstrained subtype is used.

gaussdb=# DECLARE
     SUBTYPE sint IS INT;
     a sint := 2147483647;
 BEGIN
     DBE_OUTPUT.PUT_LINE('a = ' || a);
 END;
 /
a = 2147483647
ANONYMOUS BLOCK EXECUTE

Example 2: Subtypes support typmod, range, and NOT NULL constraints.

-- typmod constraint
gaussdb=# DECLARE
     SUBTYPE sdec IS DECIMAL(3,2) NOT NULL;
     a sdec := 1.1;
     b sdec(5,2) := 322.1;
 BEGIN
     DBE_OUTPUT.PUT_LINE('a = ' || a);
     DBE_OUTPUT.PUT_LINE('b = ' || b);
 END;
 /
a = 1.10
b = 322.10
ANONYMOUS BLOCK EXECUTE
-- NOT NULL constraint
gaussdb=# DECLARE
     SUBTYPE sint IS INT NOT NULL;
     a sint;
 BEGIN
     NULL;
 END;
 /
ERROR:  variables declared as NOT NULL must have a default value.
CONTEXT:  compilation of PL/pgSQL function "inline_code_block" near line 2
gaussdb=# DECLARE
     SUBTYPE age IS BINARY_INTEGER RANGE 0..100 NOT NULL;
     a age := 18;
     b age := 20;
 BEGIN
     DBE_OUTPUT.PUT_LINE('Age of a:' || a);
     DBE_OUTPUT.PUT_LINE('Age of b:' || b);
 END;
 /
Age of a: 18
Age of b: 20
ANONYMOUS BLOCK EXECUTE

Example 3: Subtypes nest user-defined data types and use the base type constructor.

gaussdb=# DECLARE
     TYPE arrint IS VARRAY(10) OF INTEGER;
     SUBTYPE sarrint IS arrint;
     -- a sarrint := sarrint(1,2,3,4): An error is reported. Only the base type constructor is supported.
     a sarrint := arrint(1,2,3,4);
 BEGIN
     FOR i IN 1..4 LOOP
         DBE_OUTPUT.PUT_LINE(a(i));
     END LOOP;
 END;
 /
1
2
3
4
ANONYMOUS BLOCK EXECUTE

Example 4: Subtypes support self-nesting, and the constraint condition is updated.

-- range constraint
gaussdb=# DECLARE
     SUBTYPE sint IS INTEGER RANGE 10..99;
     SUBTYPE ssint IS sint RANGE 0..9;
     a sint := 50;
     b ssint := 5;
 BEGIN
     DBE_OUTPUT.PUT_LINE('a = ' || a);
     DBE_OUTPUT.PUT_LINE('b = ' || b);
 END;
 /
a = 50
b = 5
ANONYMOUS BLOCK EXECUTE

-- typmod constraint
gaussdb=# DECLARE
     SUBTYPE word IS VARCHAR2(5);
     SUBTYPE sentence IS word(50);
     a word := 'Tom';
     b sentence := 'Tom and Jerry';
     c sentence(8) := 'Mountain';
 BEGIN
     DBE_OUTPUT.PUT_LINE('a = ' || a);
     DBE_OUTPUT.PUT_LINE('b = ' || b);
     DBE_OUTPUT.PUT_LINE('c = ' || c);
 END;
 /
a = Tom
b = Tom and Jerry
c = Mountain
ANONYMOUS BLOCK EXECUTE

Example 5: User-defined data types nest subtypes.

gaussdb=# DECLARE
     SUBTYPE sint IS BINARY_INTEGER RANGE 0..99;
     TYPE tabint IS TABLE OF sint;
     a tabint := tabint();
 BEGIN
     a.EXTEND(10);
     a(1) := 50;
 END;
 /
ANONYMOUS BLOCK EXECUTE