Re: Slow Count-Distinct Query

>  tl;dr - How can I speed up my count-distinct query?  

You can't.

Doing a count(distinct x) is much different than a count(1), which can simply scan available indexes. To build a distinct, it has to construct an in-memory hash of every valid email, and count the distinct values therein. This will pretty much never be fast, especially with 2M rows involved.

I could be wrong about this, and the back-end folks might have a different answer, but I wouldn't hold my breath.

--
Shaun Thomas
OptionsHouse | 141 W. Jackson Blvd | Suite 400 | Chicago IL, 60604
312-676-8870
sthomas(at)optionshouse(dot)com

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