Re: index usage in not like

On 18 February 2010 12:18, A. Kretschmer
<andreas(dot)kretschmer(at)schollglas(dot)com> wrote:
> In response to Thom Brown :
>> On 18 February 2010 11:55, AI Rumman <rummandba(at)gmail(dot)com> wrote:
>> > "Not like" operation does not use index.
>> >
>> > select * from vtiger_contactscf where lower(cf_1253) not like
>> > lower('Former%')
>> >
>> > I created index on lower(cf_1253).
>> >
>> > How can I ensure index usage in not like operation?
>> > Anyone please help.
>> >
>>
>> How many rows do you have in your table?  If there are relatively few,
>> it probably guesses it to be cheaper to do a sequential scan and
>> calculate lower values on-the-fly rather than bother with the index.
>
> That's one reason, an other reason, i think, is, that a btree-index can't
> search with an 'not like' - operator.
>

Erm.. yes. Now that you say it, it's obvious. :S

Thom