st 22. 5. 2024 v 14:37 odesílatel Peter Eisentraut <peter@eisentraut.org> napsal:
On 18.05.24 13:29, Alvaro Herrera wrote: > I want to note that when we discussed this patch series at the dev > meeting in FOSDEM, a sort-of conclusion was reached that we didn't want > schema variables at all because of the fact that creating a variable > would potentially change the meaning of queries by shadowing table > columns. But this turns out to be incorrect: it's_variables_ that are > shadowed by table columns, not the other way around.
But that's still bad, because seemingly unrelated schema changes can make variables appear and disappear. For example, if you have
SELECT a, b FROM table1
and then you drop column b, maybe the above query continues to work because there is also a variable b. Or maybe it now does different things because b is of a different type. This all has the potential to be very confusing.
In the described case, the variable's shadowing warning will be raised.
There are more cases where not well designed changes (just with tables) can break queries or change results. Adding columns can be a potential risk, creating tables or dropping tables (when the search path contains more schemas) too.
Good practice is using well designed names and almost all use aliases or labels, and it is one way to minimize real risks. Personally I prefer a very strict mode that disallows shadowing, conflicts, ... but on second hand, for some usual work this strict mode can be boring, so we should find some good compromise.
