How do you select only the maximum version of a list of documents that have different versions in SQL?

问题

I have a database table that looks like this:

| ID | TITLE | VERSION | 
| 1  | file1 |    1    |
| 2  | file2 |    1    |
| 3  | file1 |    2    |
| 4  | file2 |    2    |

I need an SQL query that will return rows 3 and 4 because they are the latest versions of file1 and file 2.

If I run the query on a table that looks like this:

| ID | TITLE | VERSION | 
| 1  | file1 |    1    |
| 2  | file2 |    1    |
| 3  | file1 |    2    |
| 4  | file2 |    2    |
| 5  | file3 |    1    |

It should return rows 3,4 and 5 because "file3" version1 is the latest version of file3.

I know I need to use "MAX" function in SQL, however I'm getting throw off with the "GROUP BY" keyword. I'm not very familiar with how to use it.

Would appreciate all / any advice!

We are using Oracle 11g.

回答1:

Indeed, use a subquery to obtain the MAX version, grouped by TITLE, and then join the result of it with your table to obtain the ID:

SELECT t.*
FROM tbl t INNER JOIN 
     (SELECT title, MAX(version) version
      FROM tbl
      GROUP BY title
     ) max_t ON (t.version = max_t.version AND t.title = max_t.title);

DEMO.

回答2:

Actually the best way to do this is using the ranking functions:

select id, title, version
from (select t.*
             row_number() over (partition by id order by version desc) as seqnum
      from t
     ) t
where seqnum = 1

The function row_number() is called an analytic function in Oracle. It assigns number 1, 2, 3 . . . to each row, based on the partitioning clause. The numbers start over at each id, and the largest version starts at 1.

来源：https://stackoverflow.com/questions/12397330/how-do-you-select-only-the-maximum-version-of-a-list-of-documents-that-have-diff

标签

sql

oracle11g