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mysql - 合并 MySQL SELECT 语句

问题描述

我有下表tbl_crps，请注意列crp出现多次，但id和starts_on在具有相同crp的记录中总是不同的。

id |  crp | starts_on  |
------------------
1  |  20  | 2020-02-09 |
2  |  31  | 2019-06-05 |
3  |  20  | 2018-01-10 |
4  |  31  | 2021-07-03 |
5  |  58  | 2022-01-01 |
6  |  58  | 2025-02-02 |

我需要提取具有以下条件的记录：

  1. 如果对于crp存在一个或多个具有过去starts_on的记录，则必须返回具有该crp的那些记录中具有最大 id 的记录（具有过去日期的记录）

  2. 如果对于crp不存在具有过去日期的记录，则在具有该crp的所有记录中具有最大 id 的记录

我可以成功选择与以下第一个条件匹配的记录。

SELECT * FROM tbl_crps AND id IN (SELECT MAX(b.id) FROM tbl_crps b WHERE b.starts_on <= "2020-10-02")

将返回 ID 为 3 和 2 的记录。

我需要实现的是将那些starts_on不在过去且crp不在第一个结果集中的记录添加到结果中。

可能吗？也许这样？

SELECT * FROM tbl_crps a
WHERE id IN (
     SELECT MAX(a.id) FROM tbl_crps a WHERE a.starts_on <= "2020-10-02" GROUP BY a.crp
 )
UNION
(
    SELECT * FROM tbl_crps b
        WHERE id IN (
             SELECT MAX(c.id) FROM tbl_crps c WHERE c.starts_on > "2020-10-02"
             AND c.crp NOT IN (
                  SELECT d.crp FROM tbl_crps d
                  WHERE id IN (
                       SELECT MAX(e.id) FROM tbl_crps e WHERE e.starts_on <= "2020-10-02" GROUP BY e.crp)
                   )
        )
)

我正在使用 MySQL 5.7

标签： mysqlmysql-5.7

解决方案

我不确定我是否完全理解您的要求，但我认为这个查询可以满足您的需求，或者非常接近它：

WITH cteData AS (SELECT b.CRP, MAX(b.ID) AS ID
                   FROM tbl_crps b
                   WHERE b.starts_on <= "2020-10-02"
                   GROUP BY b.CRP)
SELECT *
  FROM tbl_crps a
  WHERE a.ID IN (SELECT ID
                   FROM (SELECT b.CRP, b.ID
                           FROM cteData b
                         UNION
                         SELECT d.CRP, d.ID
                           FROM tbl_crps d
                           WHERE d.starts_on > "2020-10-02" AND
                                 d.CRP NOT IN (SELECT crp
                                                 FROM cteData)) c)

这返回

id  crp starts_on
2   31  2019-06-05
3   20  2018-01-10
5   58  2022-01-01
6   58  2025-02-02

根据我对要求的理解，这似乎是正确的。简而言之

1 - NOT included because its date is in the past ('current' date = 2020-10-02) 
    and its ID is NOT the greatest among records in the past with that CRP.
2 - included because its date is in the past and its ID is the greatest
    among records with that CRP which have dates in the past.
3 - date is in the past, ID is greatest for that CRP with date in the past
4 - NOT included because date is in the future, but CRP is included in recs
    from first subquery.
5 - date is in the future, and CRP does not occur in first subquery
6 - date is in the future, and CRP does not occur in first subquery

db<>在这里摆弄

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