First some of the things that you need to use and
understand
Explain Syntax
Order by Optimization
Group by Optimization
Update: Updated errors.
Now some details that are usually missed. GROUP BY does sorting
unless you tell mysql not to. GROUP BY has two optimization
methods, loose index scan, and tight index scan.
Loose index scan, scans the entire table index, while tight index
scan uses some sort of constraint. For large datasets that are
accessed often and require some sort of group by, tight index
scans are better.
So how to pick columns to create …
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