CHECK CONSTRAINTS

CHECK CONSTRAINTS

1. Defines a condition that each row must satisfy

2. To satisfy the constraint each row in the table must make the condition either true or unknown

3. check constraints do not work on mutually exclusive concept

   • So declaring check constraints as composite check constraints is meaning less
   • UPPER(COLUMN A,COLUMN B)
     • Both Should Have Upper Case Here. Any One Should Have Upper case is Not A Rule

4. you can always declare [ column 3 value > column 1 value ] with in the same table but you cannot say this with in the different tables.

   • this means check constraints cannot behave like foreign keys
   • Check Constraints Don't have the authority to take the data from another table and cross verify

5. check constraints defines what exactly the condition you need to satisfy with every record.

6. constraint never corrects the rule, It only checks the rule

7. If The Work Is Not Happening Through check constraints then alternatives are -----

   • TRIGGERS Are The Solutions
     • After triggers programming is the solution.

8. A Single Column Can Have Multiple Number of Check Constraints.

9. NOT POSSIBLE THROUGH CHECK CONSTRAINTS

   • CHECK CONSTRAINT CANNOT TAKE DATA FROM ANOTHER TABLE THROUGH QUERIES AND START WORKING
   • YOU CANNOT WRITE A CHECK CONSTRAINT DIRECTLY ON SYSDATE, USERID, USERENV
   • THE PSUEDO COLUMNS CURVAL, NEXTVAL,, LEVEL OR ROWNUM CANNOT BE USED WITH CHECK CONSTRAINTS
   • DATE CONSTANT THAT IS NOT FULLY SPECIFIED
     • YOU CANNOT WRITE LIKE THIS : TRANSACTION SHOULD BE EQUAL TO MONTH OF MARCH

10. CHECK CONSTRAINTS HAS TWO STATES

    • ENABLE
      • THE MOMENT YOU DECLARED CONSTRAINT BY DEFAULT IT IS IN ENABLED STATE
    • DISABLE
      • SOME TIMES WHEN FUNDAMENTAL MAINTAINENCE IN THE COMPANY IS THERE THEN WE WILL DISABLE THE CONSTRAINTS.