and 'exactly this way because you do not know the value of ID_MASTER then want all ID_MASTER without have index based on ID_PARAM. hello
-------Messaggio originale------- Da: Mark Rotteveel [email protected] [firebird-support] Data: 20/07/2015 15.57.13 A: [email protected] Oggetto: Re: Rif: [firebird-support] Re: Is it possible to use only "part" of the index? 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 [Non-text portions of this message have been removed]
