SQL左连接问题

Question

表1

Id   value 
1    1 
1    4 

表2

id  Detailid   value 
1  1     1 
1  2     2 
1  3     3 
1  4     4 
1  5     5 
1  6     6 

我想要的结果

Id  Detaild  value 
1  1   1 
1  2   null 
1  3   null 
1  4   4 
1  5   null 
1  6   null 

我下面的查询给了我与空2个多余的行

select distinct t1.id,t2.detailid 
,case when t1.value IN(t2.Value) then t1.value else null end as value 
from table1 t1 
left outer join table2 t2 
on t1.id= t2.id 

我越来越

Id  Detaild value 
1  1   null ----dont need 
1  1   1 
1  2   null 
1  3   null 
1  4   null ---dont need 
1  4   4 
1  5   null 
1  6   null 

Answer 1

从你所给出的数据，这个查询会做的伎俩：

SELECT isnull(t1.Id,1), t2.Detailid, t1.value 
FROM Table2 AS t2 
LEFT OUTER JOIN Table1 AS t1 ON t1.Detailid = t2.Detailid AND t1.ID = 1 

SQLFIDDLE：http://www.sqlfiddle.com/#!3/4c808/8/0

编辑：

那么看看下面的查询，基于你上次编辑：

SELECT t2.Id, t2.Detailid, t1.value 
FROM Table2 AS t2 
LEFT OUTER JOIN Table1 AS t1 ON t1.Id = t2.Id AND t1.value = t2.value 
WHERE t2.Id = 1 

SQLFIDDLE：http://www.sqlfiddle.com/#!3/94f21a/5/0

重新编辑：

SELECT t2.Id, t2.Detailid, t1.value 
FROM Table2 AS t2 
LEFT OUTER JOIN Table1 AS t1 ON t1.Id = t2.Id AND t1.value = t2.value 
WHERE t2.id IN (SELECT Id FROM Table1) 

SQLFIDDLE：http://www.sqlfiddle.com/#!3/beede/7/0

如果(SELECT Id FROM Table1)返回太多行，你可以试试这个：

SELECT DISTINCT t2.Id, t2.Detailid, t1.value 
FROM Table2 AS t2 
INNER JOIN Table1 AS t ON t.Id = t2.Id 
LEFT OUTER JOIN Table1 AS t1 ON t1.Id = t2.Id AND t1.value = t2.value 

SQLFIDDLE：http://www.sqlfiddle.com/#!3/beede/9/0

Answer 2

那是因为你没有在表1的行与外键DetailId 2和3，因此它还能如何返回那些在加入？

Answer 3

SELECT t1.Id, t1.DetailId, t1.value 
FROM table1 AS t1 
LEFT JOIN table2 AS t2. ON t1.Detaild = t2.detailid; 

使用上述查询。

Answer 4

SELECT t1.Id, t2.DetailId, t1.value 
FROM table1 AS t1 
LEFT OUTER JOIN table2 AS t2. ON t1.DetailId = t2.detailId 
WHERE t2.DetailId NOT IN (5,6); 

Answer 5

select t2.[Id],t2.Detailid,t1.value 
from Table2 t2 
left join Table1 t1 
on t2.value = t1.value; 

FIDDLE