Question

我有这两组数据

CNU       RENT       NBED   CATEGORY
--- ---------- ---------- ----------
101        200          2          3
102        220          3          3
103        180          2          2
104        120          1          1
105        300          3          4
106        350          3          4
107        360          3          4
108        400          4          4
109        500          3          5
110        600          4          5



AID EID CNU SID ADATE          HOURS
--- --- --- --- --------- ----------
a01 e08 101 s02 15-MAY-14          3
a02 e03 101 s03 16-MAY-14          4
a03 e02 102 s02 17-MAY-14          2
a04 e09 103 s01 14-MAY-14          3
a05 e06 105 s05 18-MAY-14          5
a06 e06 107 s04 15-MAY-14          3
a07 e03 108 s04 18-MAY-14          4
a08 e09 109 s01 20-MAY-14          5
a09 e08 106 s06 15-MAY-14          3
a10 e10 102 s04 15-MAY-14          2
a11 e02 110 s04 15-MAY-14          4
a12 e10 103 s05 15-MAY-14          5
a13 e05 105 s04 16-MAY-14          4
a14 e10 107 s04 17-MAY-14          3
a15 e09 110 s01 18-MAY-14          3

我希望能够显示3类和4类的EID。

所以输出看起来像这样

EID
---
e03
e08
e10
e02

这是我到目前为止使用的代码

SELECT EID 
FROM Assignment15
JOIN Cottage15
ON Assignment15.Cnum = Cottage15.Cnum
WHERE Category=3  
AND EXISTS (SELECT Category
            FROM Cottage15
            WHERE Category=Cottage15.Category
            AND Category=4);

结果给了我一个额外的EID

EID
---
e03
e08
e10
e02

e02是额外的。我不确定什么可以调整，但如果我能得到一个适用于此的代码，那将是一个很大的帮助。非常感谢您提前

Answer 1

您只需使用IN关键字：

即可

SELECT EID 
 FROM Assignment15
 JOIN Cottage15 ON Assignment15.Cnum = Cottage15.Cnum
 WHERE Category IN (3,4) 
 GROUP BY EID
 HAVING COUNT(DISTINCT Category) = 2

请注意，在某些DBMS上，您还可以在USING条件下使用JOIN关键字，这将导致

SELECT EID 
 FROM Assignment15
 JOIN Cottage15 ON USING(Cnum)
 WHERE Category IN (3,4) 
 GROUP BY EID
 HAVING COUNT(DISTINCT Category) = 2

Answer 2

您可以使用聚合和having：

来解决此问题

select a.eid
from Assignment15 a join
     Cottage15 c
     on a.Cnum = c.Cnum
where c.Category in (3, 4)
group by a.eid
having count(distinct c.category) = 2 ;

SQL - 查找单个值是否满足一列的条件

2 个答案: