Re: help~the statement don't use index

[Øystein Grøvlen]

If MySQL uses the index to execute this query, it will have to do look-ups into the table for every row where StartDate is within the specified dates. If the Optimizer estimates that there will be very many rows within those dates, it will use a table scan instead. This is because, at least in a traditional disk-bound database, sequential access is much cheaper than random look-ups.

If you create an index (StartDate, Result, RoundSerial), the query could be executed without table look-ups since all relevant columns will be part of the query.

Øystein Grøvlen,
Senior Principal Software Engineer,
MySQL Group, Oracle,
Trondheim, Norway