SQL SERVER Topic

CHECK Constraint IN SQL
  1. The CHECK constraint is used to limit the value range that can be placed in a column.
  2. If you define a CHECK constraint on a single column it allows only certain values for this column.
  3. If you define a CHECK constraint on a table it can limit the values in certain columns based on values in other columns in the row.


How to create CHECK Constraint on TABLE in SQL:- 

  

------------CHECK Constraint for single column------------
CREATE TABLE tblEmployees 
(
EmpID INT NOT NULL CHECK (EmpId>0),
EmpName VARCHAR(100),
Address varchar(200),
MobileNo bigint,
Email NVARCHAR(200)
)

---------------CHECK Constraint for multiple columns-------------

CREATE TABLE tblEmployees
(
EmpID INT PRIMARY KEY,
EmpName VARCHAR(100),
Address varchar(200),
MobileNo bigint,
Email NVARCHAR(200),
CONSTRAINT chk_tblEmployee CHECK (EmpID>0 AND Email='sa@gmail.com')
)


How to Alter CHECK Constraint on TABLE in SQL:- 
  

------------CHECK Constraint Alter for single column------------
ALTER TABLE tblEmployees ADD CHECK (EmpID>0)

---------------CHECK Constraint Alter for multiple columns-------------

ALTER TABLE tblEmployees ADD CONSTRAINT chk_tblEmployee CHECK (EmpID>0 AND Email='sa@gmail.com')


How To DROP a CHECK Constraint in SQL:- 
  

ALTER TABLE tblEmployees DROP CONSTRAINT chk_tblEmployee