From: | Bruce Momjian <maillist(at)candle(dot)pha(dot)pa(dot)us> |
---|---|
To: | tgl(at)sss(dot)pgh(dot)pa(dot)us (Tom Lane) |
Cc: | pgsql-hackers(at)hub(dot)org |
Subject: | Re: [HACKERS] "internal error" triggered by EXISTS() |
Date: | 1998-07-15 02:45:30 |
Message-ID: | 199807150245.WAA02896@candle.pha.pa.us |
Views: | Raw Message | Whole Thread | Download mbox | Resend email |
Thread: | |
Lists: | pgsql-hackers |
We only support subqueries in the target list. May have that expaned
for 6.4.
> 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
>
>
--
Bruce Momjian | 830 Blythe Avenue
maillist(at)candle(dot)pha(dot)pa(dot)us | Drexel Hill, Pennsylvania 19026
+ If your life is a hard drive, | (610) 353-9879(w)
+ Christ can be your backup. | (610) 853-3000(h)
From | Date | Subject | |
---|---|---|---|
Next Message | Dirk Elmendorf | 1998-07-15 03:02:24 | FW: MaxQuery Plan |
Previous Message | Vadim Mikheev | 1998-07-15 02:41:09 | Re: [HACKERS] "internal error" triggered by EXISTS() |