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

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@candle.pha.pa.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)