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Domains in PSQL
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Function:
Allow usage of domains in PSQL.

Author:
Adriano dos Santos Fernandes <adrianosf@uol.com.br>

Syntax rules:
data_type ::=
<builtin_data_type>
| <domain_name>
| TYPE OF <domain_name>

Examples:
CREATE DOMAIN DOM AS INTEGER;

CREATE PROCEDURE SP (I1 TYPE OF DOM, I2 DOM) RETURNS (O1 TYPE OF DOM, O2 DOM)
AS
DECLARE VARIABLE V1 TYPE OF DOM;
DECLARE VARIABLE V2 DOM;
BEGIN
END

Notes:
1. TYPE OF gets only the type of the domain. It doesn't use constraints and default values.
2. A new field RDB$VALID_BLR was added in RDB$RELATIONS and RDB$TRIGGERS to store if the procedure/trigger is valid or not after an ALTER DOMAIN.
3. The value of RDB$VALID_BLR is shown in ISQL commands SHOW PROCEDURE/TRIGGER.