Constraints in SQL are used to define rules for the table ... #FOREIGN KEY constraint at Column Level ALTER table user_detail add FOREIGN KEY (uid) REFERENCES user_detail(uid); NOT NULL constraint: ...

In MySQL, the NOT NULL constraint is used to restrict a column to NOT accept NULL values. The NOT NULL constraint allows a column to always contains a value which means you cant not insert/update a ...

Examples to Understand MySQL NOT NULL Constraint: -- To understand this concept, first, let us create the StudentDB database and Student table by executing the below SQL Script. The above image shows ...

SQL will see combination of two columns to be unique in case of composite primary key. PK constraint will look for combination of two columns-- We cannot create PK constraint in nullable column. We ...