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"internal error" triggered by EXISTS()

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: pgsql-hackers(at)hub(dot)org
Subject: "internal error" triggered by EXISTS()
Date: 1998-07-14 21:31:36
Message-ID: 17025.900451896@sss.pgh.pa.us (view raw or flat)
Thread:
Lists: pgsql-hackers
I tried the following to find out whether a table has any records
with field1 < X (for a constant X):

tgl=> SELECT EXISTS(SELECT * FROM table WHERE field1 < X);
ERROR:  internal error: do not know how to transform targetlist

Is this a bug?  (I'm using development sources from yesterday.)

Am I using EXISTS() incorrectly?  The examples I've been able to find
only show it as a part of a WHERE clause.

If it did work, would it be any faster than a table scan?  The code
I was hoping to replace is like this:
	SELECT COUNT(field1) WHERE field1 < X;
	// test whether result > 0
Since aggregates aren't optimized very well, this ends up reading
much or all of the table, even if there is an index for field1.
I was hoping EXISTS() might be smarter...

			regards, tom lane

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Subject: Re: [HACKERS] "internal error" triggered by EXISTS()
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