MySQL Constraint – DEFAULT

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

What is DEFAULT Constraint?

MySQL DEFAULT constraint sets a default value for a column when the insert into statement does not provide a specific value. Default constraint helps you assign a particular default value to every row of a column.  Only if specifically indicated DEFAULT constraint has been applied then a value different from the default can be stored in a field.

Following is the CREATE TABLE statement with DEFAULT constraint syntax:

CREATE TABLE table_name (

                                            column1_name data type () DEFAULT,

                                            column2_name data type () DEFAULT,

                                            column1_name data type () DEFAULT

):

Example of CREATE TABLE statement with DEFAULT constraint:

So we will create here Employee table with CREATE TABLE statement and I will set a default value for address column is ‘USA’.

CREATE TABLE EMPLOYEE (

                                            EID INT NOT NULL,

                                            First_Name VARCHAR (255),

                                            Last_Name VARCHAR (255),

                                            Address VARCHAR (255) DEFAULT ‘AUS’

);

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

The syntax for add DEFAULT constraint with ALTER TABLE statement:

                              ALTER TABLE table_name

                              ALTER column_name SET DEFAULT values

Example of add DEFAULT constraint with ALTER TABLE statement on Employee Table:

                              ALTER TABLE EMPLOYEE

                              ALTER Address SET DEFAULT ‘AUS’

DROP DEFAULT constraint with ALTER TABLE statement on Employee table:

ALTER TABLE EMPLOYEE

                              ALTER Address DROP DEFAULT

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