adding not null constraint in sql server code example
Example 1: Change A filed to not null
ALTER TABLE
clients
ALTER COLUMN
phone
NVARCHAR(20) NOT NULL;
Example 2: sql is not null
The reverse of NULL. Tests for values that aren’t empty / NULL
"Tests for empty (NULL) values.
Example: Returns users that haven’t given a contact number.
SELECT * FROM users
WHERE contact_number IS NULL;"