SQL: Filter rows with max value

Question

This is my table structure:

File    |   Version     |   Function
1       |   1           |   1
1       |   2           |   1
1       |   3           |   1
1          


        

Answer 1

An efficient way to do this is often to use not exists:

select t.*
from table t
where not exists (select 1
                  from table t2
                  where t2.file = t.file and t2.Version > t.version
                 );

This query can take advantage of an index on table(file, version).

This rephrases the query to be: "Get me all rows from the table where the corresponding file has no larger version."

Answer 2

Note that this will return multiple rows per file if the overall latest version for a file exists for different functions. i.e. if your example above had an additional row (1,3,2) this would return 2 rows for file 1.

select
    t1.file,
    t1.version,
    t1.function
from 
    mytable t1
join (
    select 
        t2.file,
        max(t2.version) max_version        
    from  mytable t2
    group by t2.file
) t3 join t1.file = t3.file and t1.version = t3.max_version

Answer 3

In SQLite 3.7.11 or later, when you use MAX, the other values are guaranteed to come from the row with the largest value:

SELECT File,
       MAX(Version) AS Version,
       Function
FROM MyTable
GROUP BY File