Constraints | Types of Constraints | How to use UNIQUE and Not Null Constraint in SQL | Oracle
Constraints can define the scalability, flexibility and integrity of your database data and its apply specific rules to data,
Types of Constraints:
1.Check - If you define a CHECK constraint on a column/ table it will allow only certain values for this column / table
2.Not NULL - system will not allow null values
3.Primary key
4.Unique - it will not allow duplicate values
5.Foreign Key