On 20 Jul 2015 05:20:31 -0700, "[email protected] [firebird-support]" <[email protected]> wrote: > So, if I change the order of fields in the index I can speed things up. > Could someone explain me why it works like it works? What are the internals > behind this?
Simplified the index entry is <value of ID_MASTER><value of ID_PARAM> This means that when you only want to find ID_PARAM, then the index cannot be used, because Firebird would have to scan the whole index. If you reverse the order of the fields, you get <value of ID_PARAM><value of ID_MASTER> This means that it can quickly identify the fields with ID_PARAM (a prefix match on the entire index entry). Mark
