mysql - 查询在 mySql 中工作而不在 Oracle 中工作

Question

下面是在 MySQL 中有效但在 Oracle 中无效的查询。在这里我需要从表 r 中获取最新的日期和相应的事件 对于表 a 中的每个 ID。 ID 是唯一的。

---

 SELECT a.name , a.spids , a.group , a.id , r.date,r.event  FROM a
    LEFT OUTER JOIN ( SELECT id, MAX(date) AS latest FROM r  GROUP BY id ) AS rev
        ON rev.id = a.id
    LEFT OUTER JOIN r  ON r.id = rev.id
       AND r.date = rev.latest
     group by a.id order by ID;
    --------------------------------------------- 
    *The error in Oracle is "Not a group by function"
    I read several blogs about group by function and every where they are saying to use an aggregate funciton like sum , min,max. I tried but not able to get the results*
    -----------------------
    Table a ( It has other column - group also)
    -----------------------


   ID  Name   Spids  
    1   SIML    TRDR,THYU
    2   SIML    YUIL
    3   ghhe    yhgu,hjuy,kiuj
    4   th      yuio


   ----------------------- 
    Table r  ( Needs to get the latest updated date and corresponding event details for every ID)
    ----------------------- 


   ID     Event         Date
    1      by chris      02-02-2016
    1      by Steve      02-02-2013
    1      by gen        02-02-2014
    2      by Pete       12-12-2018
    2      by ken        01-02-2014
    3      by Mike       20-08-2018
    3      by chin       20-08-2017
    4      by chn        04-06-2012
    4      by tink       06-06-2017

---

Output should be like this ---------------------------

NAMe     SPIDS           GROUP      ID      DATE                  EVENT
    SIML    TRDR,THYU        Test        1    02-02-2016             by chris
    SIML    YUIL             Test        2    12-12-2018             by Pete 
    ghhe    yhgu,hjuy,kiuj   Test2       3    20-08-2018             by Mike
    th      yuio             Test1       4    06-06-2017             by tink

Answer 1

您的选择是:

select a.name , a.spids , a.group , a.id , r.date, r.event

您的分组依据是:

 group by a.id

这些是不兼容的——除了 a.id 之外，select 中所有其他列的值是什么。 MySQL 支持这是数据库的一个(错误的)特性，几乎任何其他数据库都不支持。

最典型的解决方案是修复这些，使它们兼容:

select a.name, a.spids, a.group, a.id, max(r.date), max(r.event)

您的分组依据是:

 group by a.name , a.spids , a.group , a.id

在您的情况下，可能根本不需要 group by:

SELECT a.name, a.spids, a.group, a.id, r.date, r.event  
FROM a LEFT OUTER JOIN
     (SELECT id, MAX(date) AS latest
      FROM r
      GROUP BY id
     ) rev
     ON rev.id = a.id LEFT JOIN
     r 
     ON r.id = rev.id  AND r.date = rev.latest
ORDER BY ID;

只有当有多行具有相同的最大日期时才需要它。

Oracle 中最常见的解决方案解决了这个问题:

SELECT a.name, a.spids, a.group, a.id, r.date, r.event  
FROM a LEFT JOIN
     (SELECT r.*,
             ROW_NUMBER() OVER (PARTITION BY r.id ORDER BY r.date DESC) as seqnum
      FROM r
     ) rev
     ON rev.id = a.id AND seqnum = 1
ORDER BY ID;