SQL Questions PART-2

Q What are different types of constraint in SQL ?

    Following are the different types of constraints in SQl:-

•     Primary Key Constraint
•     Foreign Key Constraint
•     Unique Constraint
•     Check Constraint
•     Not Null Constraint

Q What is self referencing Foreign Key ?
        When a foreign key refers to the column of the same table then it is  called self referencing foreign key.

Q what is aggregate function ?

       Aggregate function returns single value after performing calculation on        set of values.Aggregate functions are generally used with the GROUP BY        clause of the SELECT statement.

•     AVG() - It is used to find the average value
•     COUNT() - It is used to find the number of rows
•     MAX() - It is used to find the largest value
•     MIN() - It is used to find the smallest value
•     SUM() - It is used to find the sum