Question

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

I have a table of that stores versions of files and the page those files are associated with

CREATE TABLE tbl (id int, title varchar(32), version int, pageid int);
insert into tbl values (1, 'file1', 1, 25);
insert into tbl values (2, 'file2', 1, 25);
insert into tbl values (3, 'file1', 2, 25);
insert into tbl values (4, 'file2', 2, 25);
insert into tbl values (5, 'file3', 1, 25);
insert into tbl values (6, 'file1', 1, 24);
insert into tbl values (7, 'file2', 1, 24);
insert into tbl values (8, 'file1', 2, 24);
insert into tbl values (9, 'file2', 2, 24);
insert into tbl values (10, 'file3', 1, 24);

I would like to generate a query that returns to me only the maximum versions of documents that are attached to pageid=25, not pageid=24. Running the query should yield only rows 3,4,5 and not rows 8,9,10 (because they are associated with pageid=24).

I have put together a SQL Fiddle for this problem.

Answer 1

Here’s a simple query which does the trick:

select *
from tbl t1
inner join (select title, max(version) as version from tbl where pageid=25 group by 1) t2 on(t1.title=t2.title and t1.version=t2.version)
where t1.pageid=25

And here’s its SQL Fiddle output — does it do what you’re looking for?