SQL DEFAULT Constraint Tutorial

Add DEFAULT Constraint to Existing Table

Alter an existing table to add a DEFAULT constraint to a column of your choice.

Expected output: The column should have a default value applied for future inserts.

Hint: Use the ALTER TABLE statement with MODIFY or ALTER COLUMN depending on your SQL dialect.

Insert Data Without Specifying Default Column

Insert a row into a table that has a DEFAULT constraint without specifying the column with the default.

Expected output: The inserted row should contain the default value in the omitted column.

Hint: Omit the column in the INSERT statement to trigger the default value.

Experiment with DEFAULT Functions

Create a table with a datetime column that uses CURRENT_TIMESTAMP as the default and insert a row.

Expected output: The datetime column should automatically contain the current timestamp upon insertion.

Hint: Use the DEFAULT CURRENT_TIMESTAMP syntax for the datetime column.

The DEFAULT constraint provides a predefined value for a column when no explicit value is supplied during data insertion, ensuring data consistency and simplifying insert operations.

Yes, many SQL dialects allow functions like CURRENT_TIMESTAMP to be used as default values, enabling dynamic defaults such as the current date and time.

No, DEFAULT values are only applied during INSERT operations when a column value is omitted.