In MySQL stored procedures, how to check if a local variable is null?

For this, use COALESCE(). Let us implement a stored procedure to check if the local variable is null −

mysql> DELIMITER //
mysql> CREATE PROCEDURE local_VariableDemo()
   BEGIN
   DECLARE value1 int;
   DECLARE value2 int;
   select value1,value2;
   select
   concat('After checking local variable is null the sum is = ',COALESCE(value1,0)+COALESCE(value2,0));
END
//
Query OK, 0 rows affected (0.19 sec)
mysql> DELIMITER ;

Call the stored procedure using CALL command −

mysql> call local_VariableDemo();

This will produce the following output −

+--------+--------+
| value1 | value2 |
+--------+--------+
| NULL   | NULL   |
+--------+--------+
1 row in set (0.00 sec)
+-----------------------------------------------------------------------------------------------------+
| concat('After checking local variable is null the sum is = ',COALESCE(value1,0)+COALESCE(value2,0)) |
+-----------------------------------------------------------------------------------------------------+
| After checking local variable is null the sum is = 0                                                |
+-----------------------------------------------------------------------------------------------------+
1 row in set (0.01 sec)
Query OK, 0 rows affected (0.03 sec)