MySQL query that returns a specific string if column is null?

Let us first create a table −

mysql> create table DemoTable
   -> (
   -> Name varchar(100)
   -> );
Query OK, 0 rows affected (0.85 sec)

Insert some records in the table using insert command −

mysql> insert into DemoTable values('John');
Query OK, 1 row affected (0.17 sec)

mysql> insert into DemoTable values(NULL);
Query OK, 1 row affected (0.16 sec)

mysql> insert into DemoTable values(NULL);
Query OK, 1 row affected (0.20 sec)

mysql> insert into DemoTable values('David');
Query OK, 1 row affected (0.17 sec)

Display all records from the table using select statement −

mysql> select *from DemoTable;

Output

+-------+
| Name  |
+-------+
| John  |
| NULL  |
| NULL  |
| David |
+-------+
4 rows in set (0.00 sec)

Here is the query that returns a specific string if column is null −

mysql> SELECT COALESCE(Name, 'Not Valid') from DemoTable;

Output

+-----------------------------+
| COALESCE(Name, 'Not Valid') |
+-----------------------------+
| John                        |
| Not Valid                   |
| Not Valid                   |
| David                       |
+-----------------------------+
4 rows in set (0.00 sec)