Does the order of fields in a WHERE clause affect performance in MySQL?

Question

I have two indexed fields in a table - type and userid (individual indexes, not a composite).

types field values are very lim

Answer 1

Most query optimizers use the order in which conditions appear as a hint. If everything else is equal, they will follow that order.

However, many things can override that:

• the second field has an index and the first has not
• there are statistics to suggest that field 2 is more selective
• the second field is easier to search (varchar(max) vs int)

So (and this is true for all SQL optimization questions) unless you observe a performance issue, it's better to optimize for clarity, not for (imagined) performance.