DEFAULT Constraint

SQL DEFAULT Constraint

A DEFAULT constraint in SQL is used to specify a default value for a column in a table. This constraint ensures that if a value is not explicitly provided for the column when inserting a new row, the default value will be used instead.

Here's a basic example of how to use DEFAULT constraint in SQL:

 CREATE TABLE Employees (
    EmployeeID INT PRIMARY KEY,
    FirstName VARCHAR(50),
    LastName VARCHAR(50),
    Gender CHAR(1) DEFAULT 'U', -- U stands for Unknown
    HireDate DATE DEFAULT GETDATE() -- Sets default value to current date
 );
      

In this example:

• The Gender column has a DEFAULT constraint set to 'U', meaning if no gender is provided during insertion, 'U' (for Unknown) will be used as the default value.
• The HireDate column has a DEFAULT constraint set to GETDATE(), which means the current date will be used as the default value if no hire date is provided during insertion.

It's important to note that not all database systems use GETDATE(); the function for retrieving the current date might differ depending on the SQL flavor you're using. Similarly, the syntax for DEFAULT constraints can vary slightly between different database management systems.