#Function
COALESCE()
The COALESCE() function in MySQL is used to return the first non-NULL value from a list of expressions. If all expressions evaluate to NULL, then COALESCE() will return NULL. It's often used to handle NULL values in queries, replacing them with a default value or another column's value.

COALESCE(expr1,expr2,expr3)

SELECT name, COALESCE(email, 'No Email Provided') AS email
FROM users;

If the email column contains NULL for any user, 'No Email Provided' will be returned instead of NULL.

SELECT id, COALESCE(phone_home, phone_work, phone_mobile, 'No Phone Available') AS phone
FROM employees;

If phone_home is NULL, it will check phone_work, then phone_mobile, and if all of them are NULL, it will return 'No Phone Available'.

IFNULL() : - IFNULL(expression, default_value)