基于 MAX 时间戳的 SQL 内连接

Question

修改过一次

两次修改：其余 9 个表格的表头除报告外始终称为“what”。

我有大约 10 个表，结构如下：

reports (165k rows)
+-----------+-----------+
| identifier| category  | 
+-----------+-----------+
| 1         | fixed     |
| 2         | wontfix   |
| 3         | fixed     |
| 4         | invalid   | 
| 5         | later     | 
| 6         | wontfix   | 
| 7         | duplicate | 
| 8         | later     | 
| 9         | wontfix   | 
+-----------+-----------+   
 status (300k rows, all identifiers from reports come up at least once)
+-----------+-----------+----------+
| identifier| time      | what     |
+-----------+-----------+----------+
| 1         | 12        | RESOLVED |
| 1         | 9         | NEW      |
| 2         | 7         | ASSIGNED |
| 3         | 10        | RESOLVED |
| 5         | 4         | REOPEN   |
| 7         | 9         | ASSIGNED |
| 4         | 9         | ASSIGNED |
| 7         | 11        | RESOLVED |
| 8         | 3         | NEW      |
| 4         | 3         | NEW      |
| 7         | 6         | NEW      |
+-----------+-----------+----------+

 priority (300k rows, all identifiers from reports come up at least once)
+-----------+-----------+----------+
| identifier| time      | what     |
+-----------+-----------+----------+
| 3         | 12        | LOW      |
| 1         | 9         | LOW      |
| 9         | 2         | HIGH     |
| 8         | 7         | HIGH     |
| 3         | 10        | HIGH     |
| 5         | 4         | MEDIUM   |
| 4         | 9         | MEDIUM   |
| 4         | 3         | LOW      |
| 7         | 9         | LOW      |
| 7         | 11        | HIGH     |
| 8         | 3         | LOW      |
| 6         | 12        | MEDIUM   |
| 7         | 6         | LOW      |
| 6         | 9         | HIGH     |
| 2         | 6         | HIGH     |
| 2         | 1         | LOW      |
+-----------+-----------+----------+

我需要的是：

 reportsfinal (165k rows)
+-----------+-----------+--------------+------------+
| identifier| category  | what11       |  what22    |
+-----------+-----------+--------------+------------+
| 1         | fixed     | RESOLVED     | LOW        |
| 2         | wontfix   | ASSIGNED     | HIGH       |
| 3         | fixed     | RESOLVED     | LOW        |
| 4         | invalid   | ASSIGNED     | MEDIUM     |
| 5         | later     | REOPEN       | MEDIUM     |
| 6         | wontfix   |              | MEDIUM     |
| 7         | duplicate | RESOLVED     | HIGH       |
| 8         | later     | NEW          | HIGH       |
| 9         | wontifx   |              | HIGH       |
+-----------+-----------+--------------+------------+

也就是说，reports（查询后 = reportsfinal）作为基础表，我必须从其他 9 个表中添加一到两列。 identifier 是关键，但在某些表中，identifier 出现多次。在这些情况下，我只想使用时间最长的条目。 我尝试了几个查询，但没有一个有效。如果可能的话，我想使用这种方法运行一个查询以从其他 9 个表中获取不同的列。

我根据以下答案尝试了什么：

select  T.identifier,
        T.category,
        t.what AS what11,
        t.what AS what22 from (
     select R.identifier,
     R.category,
     COALESCE(S.what,'NA')what,
     COALESCE(P.what,'NA')what,
     ROW_NUMBER()OVER(partition by R.identifier,R.category ORDER by (select null))RN
     from reports R 
     LEFT JOIN bugstatus S
     ON S.identifier = R.identifier
     LEFT JOIN priority P
     ON P.identifier = s.identifier

     GROUP BY R.identifier,R.category,S.what,P.what)T
     Where T.RN = 1
     ORDER BY T.identifier;

这给出了错误：

Error: near "(": syntax error.

Answer 1

对于每个关联的表，只需使用基于子查询的谓词来识别特定的时间戳...

单字母标记 r、s 和 p 分别是表报告、状态和优先级的定义别名

Select r.Identifier, r.category,
   coalesce(s.what, 'NA') status,
   coalesce(p.what, 'NA') priority
From reports r
  left join status s
     on s.identifier = r.identifier
        and s.time =
           (Select max(time) from status 
            where identifier = r.identifier)
  left join priority p
     on p.identifier = r.identifier
        and p.time =
           (Select max(time) from priority 
            where identifier = r.identifier);

问题：为什么将列从Status 和priority 重命名为What？您不妨将其命名为 something 或 data 或 information。至少最初的名称（status 和 prio）传达了一些信息。What 这个词毫无意义。

注意。我撤消了对what11 和what12 别名的编辑，因为这些名称毫无意义。

Answer 2

基本上你需要选择列表中的相关子查询。

从臀部，类似于：

Select a.Identifier
,a.Category
,(select process
    from status where status.identifier = a.Identifer order by time desc limit 1) Process
,(select prio
    from priority where priorty.identifier = a.Identifer order by time desc limit 1) prio
From Reports a

Answer 3

根据您的假设数据使用 Row_number

select  T.identifier,
        T.category,
        what AS what11,
        what AS what22 from (
     select R.identifier,
     r.category,
     COALESCE(S.what,'NA')what,
     COALESCE(P.what,'NA')what,
     ROW_NUMBER()OVER(partition by R.identifier,r.category ORDER by (select null))RN
     from reports R left join status S
     ON S.identifier = R.identifier
     LEFT JOIN Priority P
     ON P.identifier = s.identifier

     GROUP BY R.identifier,r.category,S.what,P.what)T
     Where T.RN = 1
     ORDER BY T.identifier