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Tom Lane ff4597acd4 Allow "SET list_guc TO NULL" to specify setting the GUC to empty. ... We have never had a SET syntax that allows setting a GUC_LIST_INPUT parameter to be an empty list. A locution such as SET search_path = ''; doesn't mean that; it means setting the GUC to contain a single item that is an empty string. (For search_path the net effect is much the same, because search_path ignores invalid schema names and '' must be invalid.) This is confusing, not least because configuration-file entries and the set_config() function can easily produce empty-list values. We considered making the empty-string syntax do this, but that would foreclose ever allowing empty-string items to be valid in list GUCs. While there isn't any obvious use-case for that today, it feels like the kind of restriction that might hurt someday. Instead, let's accept the forbidden-up-to-now value NULL and treat that as meaning an empty list. (An objection to this could be "what if we someday want to allow NULL as a GUC value?". That seems unlikely though, and even if we did allow it for scalar GUCs, we could continue to treat it as meaning an empty list for list GUCs.) Author: Tom Lane <tgl@sss.pgh.pa.us> Reviewed-by: Andrei Klychkov <andrew.a.klychkov@gmail.com> Reviewed-by: Jim Jones <jim.jones@uni-muenster.de> Discussion: https://postgr.es/m/CA+mfrmwsBmYsJayWjc8bJmicxc3phZcHHY=yW5aYe=P-1d_4bg@mail.gmail.com		1 month ago
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src	Allow "SET list_guc TO NULL" to specify setting the GUC to empty.	1 month ago
KNOWN_BUGS	…
MISSING_FEATURES	…
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