RDBMS, , ,
  • 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)
                 ) ;