Question

我有这样的表

TABLE A
id | name
1  | a
2  | b
3  | c

TABLE B
id | ida | prp     | prpval
1  |  1  | visible | true
2  |  1  | active  | true
3  |  2  | visible | false
4  |  2  | active  | true
5  |  3  | visible | true
6  |  3  | active  | true

表A和表B通过id-ida连接。我想显示表A中所有名称（名称），其中表B中的属性可见（prp）设置为＆＃39; true＆＃39; （prpval）。没有任何重复。所以在这个例子中我想要显示＆＃39; a＆＃39;和＆＃39; b＆＃39;。怎么做？

Answer 1

因为你不想要重复，我会使用exists子句来解决这个问题：

select *
from tableA a
where exists (select 1
              from tableB b
              where b.ida = a.id and b.prp = 'visitor' and b.prpval = 'true'
             );

为了提高效果，请在tableB(ida, prp, prpval)上创建索引。

Answer 2

select a.name
from a
join b on a.id = b.aid
group by a.name
having sum(case when prp = 'visible' and prpvalue = 'true' then 1 else 0 end) > 0

Answer 3

一个简单的答案是：

SELECT A.name
FROM A
INNER JOIN B
ON A.id = B.ida
WHERE B.prp = 'visible'
AND B.prpval = 'true'

Answer 4

SELECT DISTINCT a.name
FROM A a join B b on a.id = b.ida
WHERE b.prp = 'visible' and b.prpval = 'true'

Answer 5

select a.name
from A as a
join  B as b on a.id=b.ida 
and b.prpval='True' and b.prp='visible'

加入两个有条件的表

5 个答案: