>>>Having done it both ways, I agree with both things you say. SET ENGINEBEHAVIOR is a hack, yes. And doing it right -- finding all the Group By clauses (trivial), changing as needed, and retesting -- can be substantial. It really depends on your future plans for the app. If it's going to still be around for a while, my tendency would be to bite the bullet and do it right.
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>I'd do it right also.
>I've done several without the SET ENGINEBEHAVIOR and they went very well.
>There were surprisingly few cases where changes were needed.
>It sounds more daunting than it is.

My experience has been that it really depends on the app. I worked on one large app where the original developer was addicted to SELECT *, so it was a lot of work to change and test those with Group By clauses.