- Business constraint defines business rules or business policy.
- Each organization have their specific rules about the data store.
- Check constraint can be used to define business rules.
Check Constraint
- When constraint cannot be define by using I/O constraints only then business constrains can be used.
- “Check” keyword is used to define business constraints.
- A check constraint takes longer time to execute compare to I/O constraint.
- It can be define as a logical expression that returns either true or false.
- Each time when a new record inserted, check constraint will be evaluate and if it returns true then record will be inserted and rejected otherwise.
- A check constraint expression must be a logical expression.
- It can also be defined either at column level or at table level.
Check constraint ( Column level )
CREATE TABLE emp ( emp_code varchar2 (4) check (emp_code like ‘C%’),
emp_name varchar2 (15) not null,
Sal number (7, 2) check (Sal>1000)
) ;
Check constraint ( Table level )
CREATE TABLE emp ( emp_code varchar2 (4),
emp_name varchar2 (15) not null,
Sal number (7, 2),
check (emp_code like ‘C %’),
check (Sal>1000)
) ;