Re: Using an ENUM column in an index

[Tom Byars]

Peter Brawley Wrote:
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> That's index selectivity = 0.0001, operationally
> indistinguishable from zero. MySQL tends to ignore
> indexes with selectivity < 0.3. Before putting
> such an index into production, I'd want to prove
> that it actually makes a positive performance
> diff.

Not sure what you mean by this Peter. Are you saying MySQL ignores the enum field and searches through all records matching the index columns that come before the enum field. e.g. Suppose I have a Tbl with primary key (Col1,Col2,Col3) and Col3 is an autoinc tinyint column to make ties on Col1,Col2 unique. What would happen there?