Conditional NOT NULL case MySQL?

For conditional NOT NULL case, you do not need to use <> and = operator. You need to use IS NULL and IS NOT NULL property because NULL is a special case in MySQL.

To understand the conditional NOT NULL case, let us create a table. The query to create a table is as follows:

mysql> create table ConditionalNotNullDemo
   -> (
   -> Id int NOT NULL AUTO_INCREMENT,
   -> SendMessage longtext,
   -> PRIMARY KEY(Id)
   -> );
Query OK, 0 rows affected (0.62 sec)

Insert some records in the table using insert command. The query is as follows:

mysql> insert into ConditionalNotNullDemo(SendMessage) values(NULL);
Query OK, 1 row affected (0.16 sec)
mysql> insert into ConditionalNotNullDemo(SendMessage) values('Hi');
Query OK, 1 row affected (0.15 sec)
mysql> insert into ConditionalNotNullDemo(SendMessage) values('Hello');
Query OK, 1 row affected (0.20 sec)
mysql> insert into ConditionalNotNullDemo(SendMessage) values(NULL);
Query OK, 1 row affected (0.18 sec)

Display all records from the table using select statement. The query is as follows:

mysql> select *from ConditionalNotNullDemo;

The following is the output:

+----+-------------+
| Id | SendMessage |
+----+-------------+
|  1 | NULL        |
|  2 | Hi          |
|  3 | Hello       |
|  4 | NULL        |
+----+-------------+
4 rows in set (0.00 sec)

Here is the demo of IS NULL and IS NOT NULL property.

Case 1: If you want to filter all NULL messages, the use IS NULL property. The query is as follows:

mysql> select *from ConditionalNotNullDemo where SendMessage IS NULL;

The following is the output:

+----+-------------+
| Id | SendMessage |
+----+-------------+
|  1 | NULL        |
|  4 | NULL        |
+----+-------------+
2 rows in set (0.00 sec)

Case 2: Use of IS NOT NULL property. If you want to display all valid messages apart from NULL message, you can use IS NULL property. The query is as follows:

mysql> select *from ConditionalNotNullDemo where SendMessage IS NOT NULL;

The following is the output:

+----+-------------+
| Id | SendMessage |
+----+-------------+
|  2 | Hi          |
|  3 | Hello       |
+----+-------------+
2 rows in set (0.03 sec)