How to use a column from joined table in a join with a subquery - sql

Question

What I'm trying to do is this:
SELECT *
FROM MainTable m
INNER JOIN JoinedTable j on j.ForeignID = m.ID
INNER JOIN (SELECT TOP 1 *
FROM SubQueryTable sq
WHERE sq.ForeignID = j.ID
ORDER BY VersionColumn DESC)
So basically, from SubQueryTable, I only want to retrieve a single row which has the maximum value for VersionColumn for all rows with a certain ID that I can get from JoinedTable.
T-SQL doesn't let me do this, what's a good way to solve this problem?
What I'm trying to prevent is loading the entire SubQueryTable and doing the filtering when it's too late as in....
SELECT *
FROM MainTable m
INNER JOIN JoinedTable j on j.ForeignID = m.ID
INNER JOIN (SELECT TOP 1 *
FROM SubQueryTable sq
ORDER BY VersionColumn DESC) sj ON sj.ForeignID = j.ID
I fear this second version performs the very slow subquery first and only filters it when it has loaded all the rows, but I want to filter sooner.
Any thoughts?

Answer 1

This will perform well if you have index on VersionColumn
SELECT *
FROM MainTable m
INNER JOIN JoinedTable j on j.ForeignID = m.ID
CROSS APPLY (SELECT TOP 1 *
FROM SubQueryTable sq
WHERE sq.ForeignID = j.ID
ORDER BY VersionColumn DESC) sj

Answer 2

Answer :
Hi,
Below query I have created as per your requirement using Country, State and City tables.
SELECT * FROM (
SELECT m.countryName, j.StateName,c.CityName , ROW_NUMBER() OVER(PARTITION BY c.stateid ORDER BY c.cityid desc) AS 'x'
FROM CountryMaster m
INNER JOIN StateMaster j on j.CountryID = m.CountryID
INNER JOIN dbo.CityMaster c ON j.StateID = c.StateID
) AS numbered WHERE x = 1
Below is your solution and above is only for your reference.
SELECT * FROM (
SELECT m.MainTablecolumnNm, j.JoinedTablecolumnNm,c.SubQueryTableColumnName , ROW_NUMBER()
OVER(PARTITION BY sj.ForeignID ORDER BY c.sjID desc) AS 'abc'
FROM MainTable m
INNER JOIN JoinedTable j on j.ForeignID = m.ID
INNER JOIN SubQueryTable sj ON sj.ForeignID = j.ID
) AS numbered WHERE abc = 1
Thank you,
Vishal Patel