1.

What are the various constraints used in Oracle?

Answer»

Once the table is created, then the user can add any value in the table, but the values have to be VALIDATED. In this case, the CONSTRAINTS act as a validator which checks the data validity.

There are five TYPES of constraints:-
  • NOT NULL:-The column will not accept the NULL value
  • UNIQUE:-It will check whether the record entered is unique or not.
  • PRIMARY:-The column will have a value, and it will be unique. In a table, only one primary key should be there.
  • CHECK:-when the user wants the record in the column to be of a PARTICULAR type.
  • FOREIGN KEY:-to relate more than one table that means matching the value of one table with that of another table.


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