Re: low cardinality column

Rong,

> I have a select like this:
>
> SELECT MAX(transactionid) FROM cbntransaction WHERE transactiontypeid=0;

Simple workaround:

Create an mulit-column index on transactiontypeid, transactionid.

SELECT transactionid FROM cbtransaction
WHERE transactiontypeid=0
ORDER BY transactionid DESC LIMIT 1;

This approach will use the index.

Of course, if the reason you are selecting the max id is to get the next id,
there are much better ways to do that.

--
-Josh Berkus
 Aglio Database Solutions
 San Francisco