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.
