试图避免重复查询

Question

我有表A作为 | name1 | name2 | value |

表B为|名|值|。

这里的“名1”，并在表A“NAME2”属性外键的表B中引用的“名”

现在我想有一个查询功能是这样的：

SELECT value FROM A WHERE name1 IN 
    (SELECT name FROM B WHERE value = '1') AND 
    name2 IN (SELECT name FROM B WHERE value = '1') 

这里的问题是，如果我不喜欢它上面的代码中，将有来自表B.两个查询，其实我只需要一个查询，有没有在SQL任何这样写道

SELECT value FROM A WHERE name1,name2 IN (SELECT name FROM B WHERE value = '1') 

而如果我想要这样的东西：

SELECT value FROM A WHERE name1,name2 IN 
    (SELECT name FROM B ORDER BY value DESC FETCH FIRST 200 ROWS ONLY) 

？

Answer 1

可以加入吗？

select value from A inner join table b b1 on a.name1 = b1.name inner join table b b2 on a.name2 = b2.name where b1.name = '1' and b2.name = '1'

Answer 2

您可以使用加入这样SELECT A.value FROM A inner join B on A.name1 = B.name inner join B on A.name2 = B.name where B.name in ('1')？

Answer 3

select name, value from b 
left outer join (select name1 from a where value = '1') as a1 on 
a1.name1 = b.name 
left outer join (select name2 from a where value = '1') as a2 on 
a2.name2 = b.name 
where value is not null 
/*omit null from left outer join for names not in table b*/ 

Answer 4

在SQLServer2005的+，你可以使用带有NOT EXISTS + EXCEPT运营商

SELECT A.value 
FROM A 
WHERE NOT EXISTS (     
        SELECT A.name1 
        UNION 
        SELECT A.name2     
        EXCEPT 
        SELECT B.name 
        FROM B 
        WHERE B.value = '1'     
        ) 

上SQLFiddle

Answer 5

演示选项创建表B中的视图，并使用它呢？

Create view B_LIMITED AS SELECT name FROM B WHERE value = '1' 

select value from A inner join table b_limited b1 on a.name1 = b1.name inner join table b_limited b2 on a.name2 = b2.name where b1.name = '1' and b2.name = '1'