2017-04-02 18:56 GMT+02:00 Fabien COELHO <coe...@cri.ensmp.fr>: > > Hello Tom, > > I'm inclined to suggest that we should require all extensions beyond the >> boolean-literal case to be set up as a keyword followed by appropriate >> argument(s); that seems like it's enough to prevent syntax conflicts from >> future additions. So you could imagine >> >> \if defined varname >> \if sql boolean expression to send to server >> \if compare value operator value >> >> It would be easy to allow "not" in front of any one of these, but >> it's less clear how to do AND or OR combinations. You can always >> fake AND with nested \if's, but OR is a bit more of a problem. >> Maybe we don't need it. >> >> Other ideas about how to design this? >> > > My 0.02 €: > > I have convinced myself that, unlike pgbench, psql does not really need an > advanced client-side-implemented language, so the smaller the better. What > I mean by this is that from psql point of view it is ok that the actual > expression evaluation is performed server-side. From a user experience > point of view it would look similar to pgbench, just the evaluator does not > need to be client-side. >
I am sorry - I disagree - I don't expect hard scripting in psql too. But psql is much more widely used than pgbench - and scripting should be intuitive. Regards Pavel > > So I would suggest something close but maybe simpler than what you suggest > above. If there is just one thing, it is true or false, checked client > side, well, this is already implemented:-). > > \if something > > If there are more than one argument, or maybe if previous true/false > evaluation failed, then: > > \if sql expression to be evaluated server side > > Then the result is checked for true or false client-side. It would be > equivalent to: > > SELECT sql expression to be evaluted server side AS is_ok \gset > \if :is_ok > > Finally I would suggest that client to server would only communicate by > variable substitution, as the backtick patch with external processes. > > For checking variable definition, I would suggest to extend the variable > access syntax so that there is no exception to the one thing rule between > client side and server side evaluation: > > \if :?variable > > the :?... is subsituted by true or false depending on whether the variable > exists. > > \if NOT :?variable > > would work by executing "NOT ..." on the server. No need for "defined" > which would not look like SQL function calls anyway, no need for any > operator client side or clumsy rules. > > -- > Fabien. > > > -- > Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) > To make changes to your subscription: > http://www.postgresql.org/mailpref/pgsql-hackers >
