SQL：对多行进行条件查询

Question

我有一张像

这样的表格

letter | number
a      | 1
a      | 1
b      | 2
c      | 1
c      | 2
c      | 2

我想编写一个SQL查询，它只返回与数字'1'和数字'2'相关联的字母值对应的行，即我只想保留

c | 1
c | 2
c | 2

来自我上面的例子。

有人可以帮忙吗？非常感谢！

Answer 1

您需要使用Group By和Having子句

这会为您提供与号码letters和1相关联的2

SELECT * 
FROM   yourtable 
WHERE  letter IN (SELECT letter 
                  FROM   yourtable 
                  WHERE  number IN ( 1, 2 ) 
                  GROUP  BY letter 
                  HAVING Count(DISTINCT number) = 2) 

• 的 SQLFIDDLE DEMO

如果您想找到与letters和1 仅关联的2，请使用此

SELECT letter 
FROM   test 
GROUP  BY letter 
HAVING Count(DISTINCT CASE WHEN number = 1 THEN 1 END) = 1 
       AND Count(DISTINCT CASE WHEN number = 2 THEN 1 END) = 1 
       AND Count(DISTINCT number) = 2 

• 的 SQLFIDDLE DEMO