Question

我尝试使用内部联接和逐个选项构建一个多选查询，我不明白为什么我的查询不起作用（我不熟悉SQL和PHP，也许这就是原因）。我收到错误消息，说明我的语法错误。

我有多个具有相同结构的表，我希望在一个查询中将一些案例按一个公共变量分组。

查询就是这样：

SELECT
    (SELECT Var1, 
    MAX( CASE WHEN Var2 ='2015' AND Var3='A1_U18' THEN Var4 ELSE 0 END ) AS 'A1_U18_0',
    MAX( CASE WHEN Var2 ='2015' AND Var3='A31_U6' THEN Var4 ELSE 0 END ) AS 'A31_U6_0'
    FROM table_a) AS a,

    (SELECT Var1,
    MAX( CASE WHEN Var2 ='2015' AND Var3='B21_U3' THEN Var4 ELSE 0 END ) AS 'B21_U3_0',
    MAX( CASE WHEN Var2 ='2015' AND Var3='B21_U6' THEN Var4 ELSE 0 END ) AS 'B21_U6_0'
    FROM table_b) AS b,

    (SELECT Var1,
    MAX( CASE WHEN Var2 ='2015' AND Var3='C21_U3' THEN Var4 ELSE 0 END ) AS 'C21_U3_0',
    MAX( CASE WHEN Var2 ='2015' AND Var3='C21_U6' THEN Var4 ELSE 0 END ) AS 'C21_U6_0'
    FROM table_c) AS c

INNER JOIN a b
    ON a.Var1 = b.Var1
INNER JOIN a c
    ON a.Var1 = c.Var1

GROUP BY a.Var1

我做错了什么？

Answer 1

您的子查询无法返回多个字段
您错过了FROM a
要声明别名，您需要使用反引号＆＃39;`＆＃39;您正在使用单引号'，这是用于字符串。

我强烈建议你做一个基本的mySql教程， This 一个帮助很多

但你可能需要这样的东西。

SELECT a.*, 
       b.`B21_U3_0`, b.`B21_U6_0`,
       c.`C21_U3_0`, c.`C21_U6_0`

FROM 
    (SELECT Var1, 
            MAX( CASE WHEN Var2 ='2015' AND Var3='A1_U18' 
                      THEN Var4 ELSE 0 END ) AS `A1_U18_0`,
            MAX( CASE WHEN Var2 ='2015' AND Var3='A31_U6' 
                      THEN Var4 ELSE 0 END ) AS `A31_U6_0`
     FROM table_a
     GROUP BY Var1
    ) AS a
JOIN    
    (SELECT Var1,
            MAX( CASE WHEN Var2 ='2015' AND Var3='B21_U3' 
                      THEN Var4 ELSE 0 END ) AS `B21_U3_0`,
            MAX( CASE WHEN Var2 ='2015' AND Var3='B21_U6' 
                      THEN Var4 ELSE 0 END ) AS `B21_U6_0`
     FROM table_b
     GROUP BY Var1 
    ) AS b
  ON a.Var1 = b.Var1
JOIN   
    (SELECT Var1,
           MAX( CASE WHEN Var2 ='2015' AND Var3='C21_U3' 
                     THEN Var4 ELSE 0 END ) AS `C21_U3_0`,
           MAX( CASE WHEN Var2 ='2015' AND Var3='C21_U6' 
                     THEN Var4 ELSE 0 END ) AS `C21_U6_0`
     FROM table_c
     GROUP BY Var1
    ) AS c
ON a.Var1 = c.Var1

带有CASE WHEN，INNER JOIN和GROUP BY1的MySQL多个SELECT查询

1 个答案: