Question

I have a table with the following basic structure.

unique_id | name | original | version
-----------------
1 | a1 | 1 | 1

2 | b1 | 2 | 1

3 | a2 | 1 | 2

4 | a3 | 1 | 3

5 | c1 | 5 | 1

6 | b2 | 2 | 2

Now it should be obvious from this that there is a form of version control, where we keep track of the original document, and also track the version of the current document.

If I want to get the latest version of a particular document I do something like the following.

SELECT * FROM table WHERE original = (SELECT original FROM table WHERE id = 3) ORDER BY version DESC

My question is, how do I do get a list of all of the most recent versions in the table with only one query?

Answer 1

The idea is to

• build a list of all original ID’s with the current maximum version
• join your table with this list of unique identifiers.

SELECT *
FROM table t
     INNER JOIN (     
       SELECT original, MAX(version) as version
       FROM tabel
       GROUP BY original
     ) tmax ON tmax.original = t.original and tmax.version = t.version