通過分組列返回特定行

Question

我堅持使用SQL查詢，其想法是我有一個數據庫，其中保存了每個文檔version(revisionNumber)等的所有文檔。我要實現的目標是，我當前只想訪問最新文檔。 revisionNumber 。

|  id | title               | documentForm | revisionNumber | effectiveDate |
| --: | ------------------- | -------------| -------------: | :------------ |
|   1 | Event Calendar      | SOP-CL       |            1.0 | 2011-02-02    |
|   2 | Event Calendar      | SOP-CL       |            2.0 | 2012-12-16    |
|   3 | Event Calendar      | SOP-CL       |            3.0 | 2014-02-15    |
|   4 | Event Calendar      | SOP-CL       |            4.0 | 2014-08-01    |
|   5 | Event Calendar      | SOP-CL       |            5.0 | 2016-09-12    |
|   6 | Event Calendar      | SOP-CL       |            6.0 | 2018-09-11    |
|   7 | Software development| SOP-DEV      |            1.0 | 2015-11-25    |
|   8 | Granting and...     | SOP-GRA      |            1.0 | 2014-08-04    |
|   9 | Granting and...     | SOP-GRA      |            2.0 | 2015-12-07    |
|  10 | Granting and...     | SOP-GRA      |            3.0 | 2018-03-26    |

在這里，您可以看到查詢后我需要得到的結果：

|  id | title               | documentForm | revisionNumber | effectiveDate |
| --: | ------------------- | ------------ | -------------: | :------------ |
|   6 | Event Calendar      | SOP-CL       |            6.0 | 2018-09-11    |
|   7 | Software development| SOP-CL       |            1.0 | 2015-11-25    |
|   3 | Granting and...     | SOP-GRA      |            3.0 | 2018-03-26    |

我一直在谷歌搜索，發現可以通過分組-例如-documentForm並返回MAX(revisionNumber)來完成，但是我沒有得到正確的行id和effectiveDate 。 我想我只是不正確地使用它們。

Answer 1

使用相關子查詢

select * from table1 t1
where revisionNumber in ( select max(revisionNumber) 
   from
   table1 t2 where t1.title=t2.title and t1.documentForm=t2.documentForm
   group by t2.title,t2.documentForm
   )

Answer 2

您可以嘗試在where子句中使用子查詢。

模式（MySQL v5.6）

CREATE TABLE t (
  title varchar(50),
  documentForm varchar(50), 
  effectiveDate date,
  revisionNumber int

);

insert into t values ('vent Calendar','SOP-CL','2011-02-02',1.0);
insert into t values ('vent Calendar','SOP-CL','2012-12-16',2.0);
insert into t values ('vent Calendar','SOP-CL','2014-02-15',3.0);
insert into t values ('vent Calendar','SOP-CL','2014-08-01',4.0);
insert into t values ('vent Calendar','SOP-CL','2016-09-12',5.0);
insert into t values ('vent Calendar','SOP-CL','2018-09-11',6.0);
insert into t values ('oftware development ','SOP-DEV','2015-11-25',1.0);  
insert into t values ('ranting and..','SOP-GRA','2014-08-04',1.0);
insert into t values ('ranting and..','SOP-GRA','2015-12-07',2.0);
insert into t values ('ranting and..','SOP-GRA','2018-03-26',3.0);

---

查詢＃1

SELECT * 
FROM t t1
WHERE revisionNumber  = (
   select max(tt.revisionNumber)
   from t tt
   WHERE t1.documentForm = tt.documentForm
);

| title                | documentForm | effectiveDate | revisionNumber |
| -------------------- | ------------ | ------------- | -------------- |
| vent Calendar        | SOP-CL       | 2018-09-11    | 6              |
| oftware development  | SOP-DEV      | 2015-11-25    | 1              |
| ranting and..        | SOP-GRA      | 2018-03-26    | 3              |

---

在數據庫小提琴上查看

Answer 3

有一個子查詢，該查詢執行GROUP BY以返回具有最高修訂版本號的每個documentForm。 JOIN該結果：

select t1.*
from tablename t1
join (select documentForm, version(revisionNumber) as maxrevisionNumber
      from tablename
      group by documentForm) t2
    on  t1.documentForm = t2.documentForm
    and t1.revisionNumber = t2.maxrevisionNumber