Put an index on time_stamp (I assume there is one on id_signal already) On 10/15/2012 12:44 PM, Pedro Jiménez wrote: > Hello, > I'm trying to do a simple SQL query over Postgresl 9.0 running on > Ubuntu. > > I have a large table (over 100 million records) with three fields, > id_signal (bigint), time_stamp (timestamp) and var_value (float). > > My query looks like this: > > select var_value from ism_floatvalues where id_signal = 29660 order by > time_stamp desc limit 1; > > So I want to select the last value from a determinated ID (is_signal). > > This query runs FOREVER, while if I delete "limit 1" it runs > instantly.... > > Any help? > > Regards. > > > >
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