Question

I have table ‘Images’ I want to get the main image if exist, and if not, get the first row in the table. I use this:

SELECT Students.Id, Images.ImagePath
FROM Students INNER JOIN    
     Images 
     ON  Students.Id = Images.StudentId 
     AND (   (Images.IsMain = 1) 
          OR (Images.ImagePath = (
              SELECT TOP(1) ImagePath 
              FROM  Images 
              WHERE StudentId = Students.IdId)))
WHERE Students.Id = @StudentId

If there is no ‘IsMain’ in Images I get only one row, but if there is ‘IsMain’, I get the row twice.

http://sqlfiddle.com/#!3/3ade7/1

Answer 1

Your problem is that you were selecting the IsMain image and the first image.

The following code selects the first row, which will be the IsMain one if it exists, otherwise the top row.

SELECT Students.Id, Images.ImagePath
FROM Students INNER JOIN    
    Images 
    ON  Students.Id = Images.StudentId 
    AND Images.ImagePath = (
        SELECT TOP(1) ImagePath 
        FROM Images 
        WHERE StudentId = Students.Id
        ORDER BY IsMain DESC) -- This line forces the IsMain image to be the top image returned.
WHERE Students.Id = 1