Re: BUG #18965: Issue with Short-Circuit Evaluation in Boolean Expressions

Jeff Davis <pgsql@j-davis.com>

From: Jeff Davis <pgsql@j-davis.com>

To: "David G. Johnston" <david.g.johnston@gmail.com>, "brandystodd@gmail.com" <brandystodd@gmail.com>, "pgsql-bugs@lists.postgresql.org" <pgsql-bugs@lists.postgresql.org>

Date: 2025-07-08T17:34:23Z

Lists: pgsql-bugs

On Fri, 2025-06-20 at 11:14 -0700, David G. Johnston wrote:
> > In the circumstance where a function evaluation is performed within
> > Boolean
> > expression, the evaluation seems to continue past a function
> > returning a
> > TRUE value.
> > 
> 
> Where did we claim we perform short-circuiting?

Even if you force the execution-time evaluation order with CASE, you
can still get an error:

EXPLAIN SELECT CASE WHEN random() < 2 THEN TRUE ELSE (1/0 = 0) END;
ERROR:  division by zero

The expression "random() < 2" is always true, so at execution time the
second branch will never be reached. But it is reached at planning
time.

Regards,
	Jeff Davis