Example
ORDER BY x ASC -- same as default
ORDER BY x DESC -- highest to lowest
ORDER BY lastname, firstname -- typical name sorting; using two columns
ORDER BY submit_date DESC -- latest first
ORDER BY submit_date DESC, id ASC -- latest first, but fully specifying order.
ASC=ASCENDING,DESC=DESCENDINGNULLscome first even forDESC.- In the above examples,
INDEX(x),INDEX(lastname, firstname),INDEX(submit_date)may significantly improve performance.
But... Mixing ASC and DESC, as in the last example, cannot use a composite index to benefit. Nor will INDEX(submit_date DESC, id ASC) help -- "DESC" is recognized syntactically in the INDEX declaration, but ignored.
