Question

我有一个像下面这样的查询结构，我想知道是否有办法将select查询写成一个使用CASE语句或其他方法，以便根据值来将值插入到适当的变量中。 / p>

DECLARE passes INT;
DECLARE fails INT;
..

SELECT count(score)
INTO passes
  FROM scores
 WHERE score >= 40;

SELECT count(score)
INTO fails
  FROM scores
 WHERE score < 40;

默多克想出了一个解决这个问题的简洁方法，我只需要对其进行一次更改，将每个值放入各自的变量中

SELECT * 
INTO   passes, fails 
FROM  (SELECT SUM(CASE 
                    WHEN score >= 40 THEN 1 
                    ELSE 0 
                  END) AS _passes, 
              SUM(CASE 
                    WHEN score < 40 THEN 1 
                    ELSE 0 
                  END) AS _fails 
       FROM   scores) AS x;

Answer 1

你可以通过为每个分数做一个案例并返回1或0来做到这一点。然后将整个事物包装在SUM（不是COUNT）中，为每个与案例匹配的实例添加一个。

SELECT 
SUM(CASE WHEN score >= 40 THEN 1 ELSE 0 END) AS passes, 
SUM(CASE WHEN score < 40 THEN 1 ELSE 0 END) AS fails 
FROM scores

Answer 2

DECLARE tpasses INT;
DECLARE tfails INT;

SELECT 
    SUM(CASE WHEN score >= 40 THEN 1 ELSE 0 END) AS passes, 
    SUM(CASE WHEN score < 40 THEN 1 ELSE 0 END) AS fails 
INTO tpasses, tfails 
FROM scores

mysql切换案例

2 个答案: