A constant declaration has two more elements:
The following code declares three constants with scalar data types.
SQL> SQL> DECLARE-- from w w w. j ava 2 s. c o m 2 credit_limit CONSTANT REAL := 5000.00; -- SQL data type 3 max_days_in_year CONSTANT INTEGER := 366; -- SQL data type 4 my_boolean CONSTANT BOOLEAN := FALSE; -- PL/SQL-only data type 5 BEGIN 6 DBMS_OUTPUT.PUT_LINE(credit_limit); 7 DBMS_OUTPUT.PUT_LINE(max_days_in_year); 8 DBMS_OUTPUT.PUT_LINE(my_boolean); 9 NULL; 10 END; 11 / DBMS_OUTPUT.PUT_LINE(my_boolean); * ERROR at line 8: ORA-06550: line 8, column 2: PLS-00306: wrong number or types of arguments in call to 'PUT_LINE' ORA-06550: line 8, column 2: PL/SQL: Statement ignored SQL>
You cannot output boolean type using DBMS_OUTPUT.PUT_LINE.