>>Is your other index (the same as combo without included column) used somewhere? I'm thinking, what if you drop that index and rely on combo index always?
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>Actually, I have always used the other way around. I do not trust those fancy indexes. I would prefer to have everything optimized with single key index. Those INCLUDE do not have my vote I have to say. Those are a pain to maintain, it took me a while to find a way to add them into the framework for their maintenances. Is their usage the only way to be optimized when we have big tables?

I think for that particular query we found that combo index is the winner. So, we get rid of other index and keep this one - at least that's how I'd try it. If the performance of other queries will decrease, we may add plain index back in.