SQL Select taking too much time to execute
I think in a million records query, you have to avoid things like OUTER JOINS. I suggest you use UNION ALL Instead of LEFT JOIN.
As long as I think CROSS APPLY is more efficient than sub-query in the select clause I will modify the query written by Conard Frix, which I think is correct. 

now: when I started to modify your query I noticed that you have a WHERE clause saying:  JoinedTable.WhereColumn IN  (1, 3). in this case, if the field is null the condition will become false. then why are you using LEFT JOIN while you are filtering null valued rows?
just replace LEFT JOIN With INNER JOIN, I guarantee that it will become faster. 

about INDEX:

please note that when you have an index on a table, say 

table1(a int, b nvarchar)


and your index is :

nonclustered index ix1 on table1(a)


and you want to do something like this:

select a,b from table1
where a &lt; 10


in your index you have not included the column b so what happens?

if sql-server uses your index, it will have to search in the index, called "Index Seek" and then refer to main table to get column b, called "Look Up". This procedure might take much longer than scanning the table itself: "Table Scan".

but based on the statistics that sql-server has, in such situations, it might not use your index at all.

so first of all check the Execution Plan to see if the index is used at all.

if yes or no both, alter your index to include all columns that you are selecting. say like:

nonclustered index ix1 on table1(a) include(b)


in this case Look Up will not be needed, and your query will execute so much faster.