Question

我有多对多的关系，我在其中查询所有具有特定N 的M，例如：

SELECT M.* FROM M INNER JOIN ManyToManyTable
ON M.Id = ManyToManyTable.M
WHERE ManyToManyTable.N = @Id

或者：

SELECT M.* FROM M INNER JOIN ManyToManyTable
ON M.Id = ManyToManyTable.M
INNER JOIN N
ON N.Id = ManyToManyTable.N
WHERE N.Id = @Id

我的问题是，如何有效地反转查询，以便所有M 没有特定的N ？

就像上面选择的NOT IN一样，但如果可能的话，没有NOT IN语句。

Answer 1

在SQL Server中，“NOT EXISTS”通常是more efficient，而不是OUTER JOIN方法。

SELECT M.* FROM M  
WHERE NOT EXISTS
 (SELECT * FROM ManyToManyTable MMT
           WHERE MMT.M = M.Id AND N=@Id )

Answer 2

又快又脏：

SELECT M.* FROM M
WHERE M.id NOT IN
    (SELECT M.id FROM M INNER JOIN ManyToManyTable
     ON M.Id = ManyToManyTable.M
     WHERE ManyToManyTable.N = @Id)

更好：

SELECT M.*
FROM M LEFT JOIN ManyToManyTable
ON M.Id = ManyToManyTable.M
WHERE ManyToManyTable.M IS NULL

如何有效地反转多对多SQL查询？

2 个答案: