MySQL 如何使用 IF 语句实现 WHILE 循环

下面是一个使用 IF 语句实现 MySQL WHILE 循环的例子。我们将在一个存储过程中使用它。

下面是创建这个存储过程的查询语句：

mysql> DELIMITER //
mysql> create procedure sp_getDaysDemo()
   -> BEGIN
   -> SELECT MONTH(CURDATE()) INTO @current_month;
   -> SELECT MONTHNAME(CURDATE()) INTO @current_monthname;
   -> SELECT DAY(LAST_DAY(CURDATE())) INTO @total_numberofdays;
   -> SELECT CAST(DATE_FORMAT(NOW() ,'%Y-%m-01') as DATE)INTO @check_weekday;
   -> SELECT DAY(@check_weekday) INTO @check_day;
   -> SET @count_days = 0;
   -> SET @workdays = 0;
   ->
   -> WHILE(@count_days < @total_numberofdays) DO
   -> IF (WEEKDAY(@check_weekday) < 5) THEN
   -> SET @workdays = @workdays+1;
   -> END IF;
   -> SET @count_days = @count_days+1;
   -> SELECT ADDDATE(@check_weekday, INTERVAL 1 DAY) INTO @check_weekday;
   -> END WHILE;  
   ->
   -> select @current_month,@current_monthname,@total_numberofdays,@check_weekday,@check_day;
   -> END
   ->
   -> //
Query OK, 0 rows affected (0.24 sec)
mysql> delimiter ;

使用 CALL 命令调用存储过程。语法如下：

CALL 你的存储过程名称();

现在可以使用以下查询语句调用存储过程：

mysql> call sp_getDaysDemo();

下面是输出结果：

+----------------+--------------------+---------------------+----------------+------------+
| @current_month | @current_monthname | @total_numberofdays | @check_weekday | @check_day |
+----------------+--------------------+---------------------+----------------+------------+
|              1 | 一月               | 31                  | 2019-02-01     |          1 |
+----------------+--------------------+---------------------+----------------+------------+
1 行记录（0.00 秒）
Query OK, 0 rows affected (0.02 sec)

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