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used_columns: EXPLAIN FORMAT=JSON tells when you should use covered indexes

MySQL Performance Blog - Mon, 14/12/2015 - 11:04pm

In the “MySQL Query tuning 101” video, Alexander Rubin provides an excellent example of when to use a covered index. On slide 25, he takes the query [crayon-566f661460fb6797259620-i/] and adds the index [crayon-566f661460fc9538594041-i/] on table [crayon-566f661460fd1535255488-i/]. With ...

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