SQL Server Query Returning Same Row Twice - sql

Question

I seem to be having trouble with the following query. It basically works, but I have a case where it is returning one row from mc_WorkoutDetails twice!
Here's the original query:
ALTER PROCEDURE [dbo].[mc_Workouts_GetActivities]
#WorkoutID bigint
AS
BEGIN
SET NOCOUNT ON
SELECT d.ID, a.Description,
CASE WHEN Reps = 0 THEN NULL ELSE Reps END AS Reps,
CASE WHEN Sets = 0 THEN NULL ELSE Sets END AS Sets,
CASE WHEN Minutes = 0 THEN NULL ELSE Minutes END AS Minutes,
d.Comments, c.Name AS Category, a.CategoryID,
(CASE WHEN v.ActivityID IS NULL THEN 0 ELSE 1 END) AS HasVideo,
a.ID AS ActivityID
FROM mc_WorkoutDetails d
INNER JOIN mc_Activities a ON d.ActivityID = a.ID
INNER JOIN mc_Activities_Categories c ON a.CategoryID = c.ID
LEFT OUTER JOIN mc_TrainerVideos v ON a.ID = v.ActivityID
WHERE (d.WorkoutID = #WorkoutID)
ORDER BY SortOrder, a.Description
RETURN ##ERROR
END
Then I tried changing:
INNER JOIN mc_Activities a ON d.ActivityID = a.ID
INNER JOIN mc_Activities_Categories c ON a.CategoryID = c.ID
To:
LEFT OUTER JOIN mc_Activities a ON d.ActivityID = a.ID
LEFT OUTER JOIN mc_Activities_Categories c ON a.CategoryID = c.ID
But that didn't seem to help. I still get the duplicate row.
Can anyone see what's happening?

Answer 1

What you can do is add a join back to the same table using a group to weed out the duplicate rows.
So add this to your join after FROM mc_WorkoutDetails d:
inner join (select [columns you want to select], max(id) id
from mc_WorkoutDetails
group by [columns you want to select] ) q on q.id = d.id
Let me know if that makes sense. Basically you are doing a distinct and getting the max id so you eliminate one of the rows in the join. You have to remember that even if you want there to be duplicates, they will be eliminated even if they are suppose to be there.
The full alter would be:
ALTER PROCEDURE [dbo].[mc_Workouts_GetActivities]
#WorkoutID bigint
AS
BEGIN
SET NOCOUNT ON
SELECT d.ID, a.Description,
CASE WHEN Reps = 0 THEN NULL ELSE Reps END AS Reps,
CASE WHEN Sets = 0 THEN NULL ELSE Sets END AS Sets,
CASE WHEN Minutes = 0 THEN NULL ELSE Minutes END AS Minutes,
d.Comments, c.Name AS Category, a.CategoryID,
(CASE WHEN v.ActivityID IS NULL THEN 0 ELSE 1 END) AS HasVideo,
a.ID AS ActivityID
FROM mc_WorkoutDetails d
inner join (select Reps, Sets, Comments, Minutes, max(id) id
from mc_WorkoutDetails
group by Reps, Sets, Comments, Minutes ) q on q.id = d.id
INNER JOIN mc_Activities a ON d.ActivityID = a.ID
INNER JOIN mc_Activities_Categories c ON a.CategoryID = c.ID
LEFT OUTER JOIN mc_TrainerVideos v ON a.ID = v.ActivityID
WHERE (d.WorkoutID = #WorkoutID)
ORDER BY SortOrder, a.Description
RETURN ##ERROR
END

Answer 2

Thanks for everyone's input. The general suggestions here were correct: I had two rows in the mc_workoutDetails table that referenced the same row in the mc_Activities table.
While the foreign key was part of a unique primary key, it was a compound key and so this column could contain duplicates as long as the other column in the key were different.