Explain NOT NULL constraint in SQL Server.

The NOT NULL constraint is used not to accept NULL values in a column. This makes sure to add values at the time of adding and updating the records.

Ex :

Create Table Suppliers

(

Supplier_ID int NOT NULL,

Supplier_Name varchar (300) NOT NULL,

Address varchar (500),

City varchar (200)

)

This Query will make sure the “Supplier_ID” and “Supplier_Name” columns to not accept NULL values.

Explain the ALTER table statement in SQL Server.

The ALTER table statement is used to add, delete or modify the columns in a table.

Ex :
To ADD a column in a table,

ALTER TABLE Employees

ADD DateofBirth date

This Query will display a new column “DateofBirth” in date format to Employees table.

To DELETE a column in a table,

ALTER TABLE Employees

DROP column DateofBirth

This Query will delete the column “DateofBirth” from Employees table.