为此,请使用COALESCE()
。让我们实现一个存储过程来检查局部变量是否为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 // mysql> DELIMITER ;
使用CALL命令调用存储过程-
mysql> call local_VariableDemo();
这将产生以下输出-
+--------+--------+ | 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)