Question

我正在寻找解决方案（MS SQL 2008，顺便说一句）：

ID | ParentID | Feature_1 | Feature_2 +-----+------------+------------+----------+ 1 | NULL | A | B 2 | 1 | A | B 3 | 1 | A | C 4 | 2 | A | C

每当一个子（具有ParentID的记录）具有与其父级相同的一组功能（Feature_1和Feature_2）时，我想忽略它，基本上不会在我的select *中显示它。

所以结果集应该是

ID | ParentID | Feature_1 | Feature_2 +-----+------------+------------+----------+ 1 | NULL | A | B 3 | 1 | A | C 4 | 2 | A | C

请注意，ID = 2会被删除，但会显示ID = 4，因为它具有与其父级不同的一组功能。

非常感谢任何帮助！

Answer 1

SELECT
    Child.ID,
    Child.ParentID,
    Child.Feature_1,
    Child.Feature_2
FROM
    MyTable AS Child
    LEFT OUTER JOIN MyTable AS Parent
        ON Child.ParentID = Parent.ID
WHERE
    Parent.Feature_1 <> Child.Feature_1
    OR Parent.Feature_2 <> Child.Feature_2
    OR Child.ParentID IS NULL
ORDER BY
    Child.ID

Answer 2

SELECT *
FROM table A
WHERE a.ParentID IS NULL OR NOT EXISTS (SELECT 1 
                 FROM table b
                 WHERE a.ParentID = b.ID
                 AND a.Feature_1 = b.Feature_1 AND a.Feature_2 = b.Feature_2)

SQL用于识别树状结构中的重复项

2 个答案: