Documentation for domains in PSQL

doc/WhatsNew

@@ -469,6 +469,8 @@
 
     * Feature CORE-660
         Domains allowed to be used in PSQL parameters and variables
+      See also:
+        /doc/sql.extensions/README.domains_psql.txt
       Contributor(s):
         Adriano dos Santos Fernandes <adrianosf at uol.com.br>
 

doc/sql.extensions/README.domains_psql.txt

@@ -0,0 +1,30 @@
+---------------
+Domains in PSQL
+---------------
+
+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 don'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 showed in ISQL commands SHOW PROCEDURE/TRIGGER.