Default in DBMS

DEFAULT clause

• Default clause in SQL is used to add default data to the columns
• When a column is specified as default with some value then all the rows will use the same value i.e each and every time while entering the data we need not enter that value
• But default column value can be customized i.e it can be overridden  when inserting a data for that row based on the requirement.

Example for DEFAULT clause 

The following SQL sets a DEFAULT value for the “city” column when the “emp” table is created:

CREATE TABLE emp (
    ID int NOT NULL,
    LastName varchar(255) NOT NULL,
    FirstName varchar(255),
    Age int,
    City varchar(255) DEFAULT 'hyderabad'
);

• You can see that all the values of the city column are  same i.e Hyderabad this is because we have set city column as default column with a default value of Hyderabad 
• As a result, whenever you insert a new row each time you need not enter a value for this default column  that is entering a column value for a default column is optional and if you don’t enter the same value is considered that is used in the default clause