Constraints in SQL
Constraints In SQL: Constraints are the rules that must be followed to enter data in the table. The constraint is just like a check that is applied to ingoing and outgoing of data in the table. It is used to check that which types of data would be entered in the table. The data that violates the constraint can’t be entered in the table. A constraint can be defined in two ways table level and column level . Table level constraint can be applied to the whole table and column level constraint can be applied to the specific column. How to apply constraint: We can apply constraint at the time of creating a table using CREATE TABLE keyword. If we want to change the constraint after applying it then we can perform updation through ALTER TABLE statement. Syntax of Constraints at Column Level : CREATE TABLE table_name ( column1 datatype constraint , column2 datatype constraint , column3 datatype constraint ); Syntax of Constraints at Table