po 31. 1. 2022 v 19:09 odesílatel Julien Rouhaud <rjuju123@gmail.com> napsal:
Hi,
On Mon, Jan 31, 2022 at 06:46:37PM +0100, Pavel Stehule wrote: > > I checked the last patch. I think it is almost trivial. I miss just > comment, why this alias is necessary > > + if (!rte->alias) > + rte->alias = makeAlias(get_rel_name(rte->relid), NULL);
Thanks for looking at it Pavel!
The alias is necessary because otherwise queries involving views won't produce valid SQL, as aliases for subquery is mandatory. This was part of the v1 regression tests:
+-- test pg_get_query_def() +SELECT pg_get_query_def('SELECT * FROM shoe') as def; + def +-------------------------------------------------------- + SELECT shoename, + + sh_avail, + + slcolor, + + slminlen, + + slminlen_cm, + + slmaxlen, + + slmaxlen_cm, + + slunit + + FROM ( SELECT sh.shoename, + + sh.sh_avail, + + sh.slcolor, + + sh.slminlen, + + (sh.slminlen * un.un_fact) AS slminlen_cm,+ + sh.slmaxlen, + + (sh.slmaxlen * un.un_fact) AS slmaxlen_cm,+ + sh.slunit + + FROM shoe_data sh, + + unit un + + WHERE (sh.slunit = un.un_name)) shoe; +
the mandatory "shoe" alias is added with that change.
I looked for other similar problems and didn't find anything, but given the complexity of the SQL standard it's quite possible that I missed some other corner case.
I don't feel good about forcing an alias. relname doesn't ensure uniqueness. You can have two views with the same name from different schemas. Moreover this field is necessary only when a deparsed query is printed, not always.
Isn't possible to compute the correct subquery alias in print time when it is missing?