Thread

1. why can't 2 indexes be used at once?

   Joseph Shraibman <jks@selectacast.net> — 2004-04-29T23:19:09Z

   Lets say I have two columns, A and B.  They are each indexed seperately. 
     If I do a query like:
   SELECT * FROM table WHERE A = 1 AND B = 2;
   postgres can only use one index.
   
   I assume that postgres uses the index data to narrow down pages in the 
   table to visit when doing its search. Then it goes through and filters 
   on the second condition.
   
   My question: why can't it go through the first index, get a list of 
   pages in the table, then go through the second index, union the result 
   with the results from first index, and then go into the table?
   
   

2. Re: why can't 2 indexes be used at once?

   Tom Lane <tgl@sss.pgh.pa.us> — 2004-04-30T03:57:49Z

   Joseph Shraibman <jks@selectacast.net> writes:
   > My question: why can't it go through the first index, get a list of 
   > pages in the table, then go through the second index, union the result 
   > with the results from first index, and then go into the table?
   
   See TODO list ...
   
   			regards, tom lane