MySQL Constraint – CHECK

MongoDB with .Net Core course link => https://www.udemy.com/mongodb-with-net-core-sagar-jaybhay/

Hello everyone in the previous article we learn about MySQL Constraint –FOREIGN KEY and in this article, we will learn CHECK constraint with example. Let’s go.

C# basic course click on: https://www.udemy.com/learn-csharp-with-sagar-jaybhay/ 

Web API 2- .Net Core In depth In 5 Hours click on: https://www.udemy.com/web-api-2-net-core-in-depth-in-5-hrs-with-sagar-jaybhay/

What is CHECK constraint?

MySQL CHECK constraint controls the values in a column satisfies a specific condition. CHECK constraint defines on a table it can limit the values on specific columns based on values in other columns in the row.

Following is the CREATE TABLE statement with CHECK constraint syntax:

                             CREATE TABLE table_name(

                                            Column1_name data type CHECK (condition)

                                            Column2_name data type CHECK (condition)

                             );

MongoDB with .Net Core course link => https://www.udemy.com/mongodb-with-net-core-sagar-jaybhay/

For define multiple columns CHECK constraint then you can use following syntax:

CREATE TABLE table_name(

                              column1_name data type ()

                              column1_name data type ()

                              CONSRTAINT constraint_name CHECK (condition AND condition)

);

C# basic course click on: https://www.udemy.com/learn-csharp-with-sagar-jaybhay/ 

Web API 2- .Net Core In depth In 5 Hours click on: https://www.udemy.com/web-api-2-net-core-in-depth-in-5-hrs-with-sagar-jaybhay/

Example of CREATE TABLE statement with a CHECK constraint:

                              CREATE TABLE EMPLOYEE (

                                            EID INT NOT NULL,

                                            First_Name VARCHAR (255),

                                            Last_Name VARCHAR (255),

                                            Age INT CHECK (Age > =25)

                              );

C# basic course click on: https://www.udemy.com/learn-csharp-with-sagar-jaybhay/ 

Web API 2- .Net Core In depth In 5 Hours click on: https://www.udemy.com/web-api-2-net-core-in-depth-in-5-hrs-with-sagar-jaybhay/

Example for define multiple column a CHECK constraint:

                              CREATE TABLE EMPLOYEE (

                                            EID INT NOT NULL,

                                            First_Name VARCHAR (255),

                                            Last_Name VARCHAR (255),

                                            Address VARCHAR (255),

                                            CONSTRAINT CHK_EMPLOYEE CHECK (Age > = 25 AND Address = ‘USA’)

                              );

MongoDB with .Net Core course link => https://www.udemy.com/mongodb-with-net-core-sagar-jaybhay/

You can add CHECK constraint when the table is already created using the ALTER TABLE statement. Following is the syntax and example:

Syntax

ALTER TABLE table_name

                              ADD CONSTRAINT constraint_name CHECK (column_name);

               Example

                              ALTER TABLE EMPLOYEE

                              ADD CONSTRAINT CHK_EMPLOYEE CHECK (Age > = 25 AND Address = ‘USA’);

If you want to DROP created a CHECK constraint, then follow the steps:

ALTER TABLE EMPLOYEE

DROP CHECK CHK_EmployeeAge;

MongoDB with .Net Core course link => https://www.udemy.com/mongodb-with-net-core-sagar-jaybhay/

C# basic course click on: https://www.udemy.com/learn-csharp-with-sagar-jaybhay/ 

Web API 2- .Net Core In depth In 5 Hours click on: https://www.udemy.com/web-api-2-net-core-in-depth-in-5-hrs-with-sagar-jaybhay/