SQL INNER JOIN基於時間戳

Question

對MAX一旦

兩次修訂後的修正：剩餘9個表，除了報告的標題往往被稱之爲「什麼」。

我有大約10個表結構如下：

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  | 
+-----------+-----------+--------------+------------+ 

也就是說，reports（後查詢= reportsfinal）作爲基礎表我必須從9個其他表中添加一列或兩列。 identifier是關鍵，但在某些表中，identifier出現多次。在這些情況下，我只想使用最高時間的條目。 我嘗試了幾個查詢，但都沒有工作。如果可能的話，我想用這種方法運行一個查詢來從其他9個表中獲取不同的列。

我試圖基於下面的答案是什麼：

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;

這給了錯誤：

Error: near "(": syntax error.

Answer 1

對於每個關聯表只使用基於子查詢謂詞確定具體的時間戳...

單字母標記R，S和P爲表報告的，狀態和優先級分別

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); 

定義別名問題：爲什麼您將Status和priority的列重命名爲What？您可能還需要something或data或information。至少原來的名字（status和prio）溝通了一些東西。單詞What是沒有意義的。

注意。我將what11和what12的別名的編輯反轉（解開），因爲這些名稱是毫無意義的。

Answer 2

基本上你需要一個在選擇列表中相關的子查詢。

從臀部，是這樣的：使用ROW_NUMBER

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

作品根據您的假設數據

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