Column constraints - NOT NULL and UNIQUE

NOT NULL Constraint

Let’s create a new table teachers, and insert a few rows of records in it.

Notice that we are able to enter a record with name as NULL in the table. What if, we want to enforce that no new record should contain name as NULL?

SQL provides NOT NULL option to add to a column definition while creating a table. It is one of the first column constraints that we are going to explore in this course. Look at the CREATE TABLE statement below.

We just have to add NOT NULL next to the column name and data type, in the list of columns in CREATE TABLE statement. This makes sure that no insert is allowed with NULL in the specified column. Try the set of statements below:

Observe that on attempting an insert with name as NULL, we get an error that expresses failing constraint.