Question

我有一张像这样的表

c_id           b_id
13              151
27              203
38              347
38              349
38              357
72              132
72              475
104             14
151             22
207             690
207             712

如您所见，该表首先由c_id排序，然后由b_id排序。 我想删除每个c_id的第一个条目。

所以我的输出表应该是这个

c_id            b_id
38              349 
38              357
72              475
207             712

只删除了与其关联的b_id的c_id。并且已删除其他c_ids的第一个b_ids。

可以使用多个查询。原始表中有数百万行。

Answer 1

SELECT cb.c_id, cb.b_id
  FROM cb
  LEFT JOIN (
    SELECT c_id, MIN(b_id) AS minb_id
      FROM cb
      GROUP BY c_id
    ) cbmin ON cb.c_id = cbmin.c_id AND cb.b_id = cbmin.minb_id
  WHERE cbmin.c_id IS NULL

Answer 2

SELECT * 
FROM 
(
    SELECT c_id, b_id, 
        ROW_NUMBER() OVER(PARTITION BY c_id ORDER BY c_id DESC) RowNum
    FROM TestTable
    WHERE c_id IN 
       (
           SELECT c_id 
           FROM TestTable 
           GROUP BY c_id
           HAVING COUNT(b_id) > 1
       )
) t WHERE RowNum > 1

这应该给你以下内容：

c_id   b_id   RowNum
--------------------
38     349     2
38     357     3
72     475     2
207    712     2

Live Demo

Answer 3

首先选择c_id

列表

SELECT c_id FROM TABLE GROUP BY c_id

获取每个c_id的第一个元素并删除

DELETE FROM TABLE 
      WHERE ID = (SELECT ID
                    FROM (SELECT ROW_NUMBER () OVER (ORDER BY ID) row_no, a.*
                            FROM TABLE a
                           WHERE a.ID = 11)
                   WHERE row_no = 1)

Answer 4

SELECT cb.c_id, cb.b_id
  FROM cb
  LEFT JOIN cb cbmin ON cb.c_id = cbmin.c_id
  GROUP BY cb.c_id, cb.b_id
  HAVING cb.b_id > MIN(cbmin.b_id)

从组中删除第一个条目

4 个答案:

Live Demo