[SQL] Help with multistage query

[Rick Schumeyer]

I have a perl script that issues a series of SQL statements to perform some queries.  The script works, but I believe there must be a more elegant way to do this.   The simplified queries look like this:   SELECT id FROM t1 WHERE condition1;   ;returns about 2k records which are stored in @idarray   foreach $id (@idarray) {    SELECT x FROM t2 WHERE id=$id;   ; each select returns about 100 records which are saved in a perl variable }   At this point I have a list of about 200k records, from which I can manually filter based on x values.   There are indices on id in both t1 and t2, so the first two queries are both index scans.  I cannot afford a table scan on t2 due to the size of the table.   Like I said, this works (and uses only index scans), but I would think it would be better to somehow select the 200k records into a temp table.  Because the temp table would be relatively small, a seq scan is ok to produce my final list.   Also, I am now issuing the second query about 2k times…this seems inefficient.   I would think there would  a way to restate the first two queries as either a join or a subselect.  My initial attempts result in a table scan (according to EXPLAIN) on t2.   For example I tried    SELECT x FROM t2 WHERE id in ( SELECT id FROM t1 WHERE condition1); but this gives a seq scan.   Any ideas are appreciated.