Question

I have a fairly simple SQL statement to get some results from a couple of tables. One of the columns is generated from an inline SQL statement. While I seem to be able to order by this column, trying to filter with it says that the column is invalid. Here is my code and error:

SELECT 
        e.Title as Title,
        -- Get earliest start time and latest end time
        (SELECT TOP 1 l.StartTime FROM Locations l WHERE l.EventID = e.EventID ORDER BY l.StartTime ASC) as EarliestStartTime,
        (SELECT TOP 1 l.EndTime FROM Locations l WHERE l.EventID = e.EventID ORDER BY l.EndTime DESC) as LatestEndTime

    FROM
        Events e
    WHERE
            e.UserID = @UserID
        AND LatestEndTime < DATEADD(DAY, GETDATE(), 1)
    ORDER BY
        EarliestStartTime ASC

Error:

Invalid column name 'LatestEndTime'.

If I remove the AND LatestEndTime < DATEADD(DAY, GETDATE(), 1) then the statement works perfectly.

Answer 1

You can’t refer to columns by alias in the where clause. Either write it out, repeating the column definition:

WHERE  e.UserID = @UserID
       AND (SELECT TOP 1 l.EndTime FROM Locations l 
            WHERE l.EventID = e.EventID ORDER BY l.EndTime DESC) < 
            DATEADD(DAY, GETDATE(), 1)

Or use a subquery to name the column:

select  *
from    (
        select  e.Title as Title,
                -- Get earliest start time and latest end time
                (SELECT TOP 1 l.StartTime FROM Locations l
                 WHERE l.EventID = e.EventID ORDER BY l.StartTime ASC)
                 as EarliestStartTime,
                (SELECT TOP 1 l.EndTime FROM Locations l
                 WHERE l.EventID = e.EventID ORDER BY l.EndTime DESC)
                 as LatestEndTime
        from    Events e
        ) as SubQuery
WHERE   UserID = @UserID
        and LatestEndTime < DATEADD(DAY, GETDATE(), 1)