Constraint

[chamarthi siva]

Dear Dudes.

Could anybody let me know what is the difference b/w Table level and column level constraint.

Not null constraint can be defined at only column level, why not at table level?






Scjp 1.4

[Mark Spritzler]

So a Table level constraint might be that two fields that have dates, lets say, and you want to make sure that the start_date is prior to the end_date, that is where only a table level contraint will work. You cannot create a column level constraint that compares to some other column.

With Null, null is a value you can put in a field, you can't put a null into a table. meaning you can't set a table to equal null.

HTH

Mark