Selectivity threshold for a non-covering index

(Vladimir Kolesnikov) Assume you have a table with about 300 000 rows, and an indexed column ecol1Πwith only 9 distinct values. Now you got a query like fselect * from t1 where col1 = constf. The questions are Рwhen the index is faster to full table scan and vice versa? Рdoes MySQL use th

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