試圖避免重複查詢

Question

我有表A作爲 | name1 | name2 | value |

表B爲|名|值|。

這裏的「名1」，並在表A「NAME2」屬性外鍵的表B中引用的「名」

現在我想有一個查詢功能是這樣的：

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

這裏的問題是，如果我不喜歡它上面的代碼中，將有來自表B.兩個查詢，其實我只需要一個查詢，有沒有在SQL任何這樣寫道

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

而如果我想要這樣的東西：

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

？

Answer 1

可以加入嗎？

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

您可以使用加入這樣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+，你可以使用帶有NOT EXISTS + EXCEPT運營商

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

演示選項創建表B中的視圖，並使用它呢？

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'