Hi,

I have a table with hierarchical data, which is stored using the
Modified Preorder Tree Traversal algorithm (MPTT).

More information about MPTT can be found here:
http://dev.mysql.com/tech-resources/...ical-data.html.

I was wondering if indexing on the lft and rgt column will have speed
advantages, as the cardinality of the index will always be the same as
the number of rows there are in the database.

In my case, there are about 40000 rows in my hierarchical data table.