Re: SEARCH and CYCLE clauses

On Fri, May 22, 2020 at 5:25 AM Peter Eisentraut
<peter(dot)eisentraut(at)2ndquadrant(dot)com> wrote:
> This is something we need to think about. If we want to check at parse
> time whether the two values are not the same (and perhaps not null),
> then we either need to restrict the generality of what we can specify,
> or we need to be prepared to do full expression evaluation in the
> parser. A simple and practical way might be to only allow string and
> boolean literal. I don't have a strong opinion here.

I don't have an opinion on this feature, but I think doing expression
evaluation in the raw parser would be a pretty bad idea. I think we're
not supposed to do anything in the parser that involves catalog access
or even references to GUC values. It might be OK if it happens in
parse analysis rather than gram.y, but even that sounds a bit sketchy
to me. We'd need to think carefully about what effects such things
woul have on the plan cache, and whether they introduce any security
holes, and maybe some other things.

--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company