

Do you use GROUP BY correctly? - donteatbark
http://www.dbasquare.com/2012/05/15/mysql-mistakes-do-you-use-group-by-correctly/

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Jare
I often include such columns during ad-hoc analytics, because it is one valid
example of the data being grouped. In particular, when COUNT(*) is 1 the value
in that column is THE value, and thanks to including it in the query, I
already have it. It's very convenient with very low cost.

For queries that are part of a formal process or application it's harder to
find a use case.

