How do I create a DESC index in MySQL?

mysql, performance

Solution

That's one of those MySQL "features" where it silently ignores your request to do something because it's simply not implemented:

From http://dev.mysql.com/doc/refman/5.5/en/create-index.html

"An index_col_name specification can end with ASC or DESC. These keywords are permitted for future extensions for specifying ascending or descending index value storage. Currently, they are parsed but ignored; index values are always stored in ascending order"

Problem

I have a table from which I need to obtain rows ordered by a field in descending order. When running an `EXPLAIN` query like the following: ``` EXPLAIN SELECT ... FROM table WHERE ... ORDER BY field DESC ``` I get `Using where; Using filesort` in the `Extra` column. So I try to create a `DESC` index: ``` CREATE INDEX name ON table (field DESC); ``` But when I run `EXPLAIN` again, I get the same `Using where; Using filesort` in the `Extra` column and the performance is pretty much the same. What am I doing wrong?

Original source