Specifying the rules that apply to SQL behavior at run time

CURRENT RULES determines the SQL rules, DB2 or SQL standard, that apply to SQL behavior at run time. For example, the value in CURRENT RULES affects the behavior of defining check constraints by issuing the ALTER TABLE statement on a populated table:

• If CURRENT RULES has a value of STD and no existing rows in the table violate the check constraint, DB2 adds the constraint to the table definition. Otherwise, an error occurs and DB2 does not add the check constraint to the table definition.

  If the table contains data and is already in a check pending status, the ALTER TABLE statement fails.

• If CURRENT RULES has a value of DB2, DB2 adds the constraint to the table definition, defers the enforcing of the check constraints, and places the table space or partition in CHECK-pending status.

You can use the statement SET CURRENT RULES to control the action that the statement ALTER TABLE takes. Assuming that the value of CURRENT RULES is initially STD, the following SQL statements change the SQL rules to DB2, add a check constraint, defer validation of that constraint, place the table in CHECK-pending status, and restore the rules to STD.

EXEC SQL
  SET CURRENT RULES = 'DB2';
EXEC SQL
  ALTER TABLE DSN8A10.EMP
    ADD CONSTRAINT C1 CHECK (BONUS <= 1000.0);
EXEC SQL
  SET CURRENT RULES = 'STD';

See Check constraints for information about check constraints.

You can also use CURRENT RULES in host variable assignments. For example, if you want to store the value of the CURRENT RULES special register at a particular point in time, you can use assign the value to a host variable, as in the following statement:

SET :XRULE = CURRENT RULES;

You can also use CURRENT RULES as the argument of a search-condition. For example, the following statement retrieves rows where the COL1 column contains the same value as the CURRENT RULES special register.

SELECT * FROM SAMPTBL WHERE COL1 = CURRENT RULES;