Maintaining order in MySQL group by results

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1

I’m trying to figure out how to get specific results from my MySQL database. Here’s what my table looks like:

TaskID | UserID | TaskName | StepNumber
-------+--------+----------+-----------
1      | 1      | JobA     | 1
2      | 1      | JobB     | 2
3      | 2      | JobC     | 3
4      | 1      | JobD     | 4
5      | 1      | JobE     | 5

What I want is this output:

UserID
------
1
2
1

But when I use GROUP BY on UserID, I just get:

UserID
------
1
2

This doesn’t keep the order I need. Is there a way to do this with one query? Or do I need something more complex? Thanks for any help!

2

I’ve dealt with similar issues before, and I found that using a subquery with UNION can be quite effective. Here’s an approach that might work for you:

SELECT UserID FROM (
    SELECT UserID, StepNumber
    FROM YourTable
    WHERE UserID = 1
    UNION ALL
    SELECT UserID, MIN(StepNumber)
    FROM YourTable
    WHERE UserID != 1
    GROUP BY UserID
) AS subquery
ORDER BY StepNumber

This query first selects all rows for UserID 1, maintaining their original order. Then it unions these results with the grouped results for other UserIDs. The final ORDER BY ensures everything stays in the correct sequence.

It’s not the most elegant solution, but it gets the job done without requiring complex window functions. Just make sure to replace ‘YourTable’ with your actual table name.

3

To achieve the desired output while maintaining the original order, you’ll need to use a combination of GROUP BY and ORDER BY clauses. Here’s a query that should work:

SELECT UserID
FROM (
    SELECT UserID, MIN(StepNumber) AS MinStep
    FROM YourTableName
    GROUP BY UserID, StepNumber
) AS subquery
ORDER BY MinStep

This query first groups the results by both UserID and StepNumber, then orders them by the minimum StepNumber for each group. This preserves the original order while still giving you the grouped results you’re looking for.

Keep in mind that this approach assumes StepNumber is unique for each UserID. If that’s not the case, you might need to adjust the query slightly, perhaps by including TaskID in the ordering.

4

hey sophiac, have u tried using ROW_NUMBER() function? it might help. something like:

SELECT DISTINCT UserID FROM (
SELECT UserID, ROW_NUMBER() OVER (ORDER BY StepNumber) as rn
FROM YourTable
) t
ORDER BY rn

this should keep the order u want. lmk if it works!