On 1/27/16, Yannick Duch?ne <yannick_duchene at yahoo.fr> wrote: > On Wed, 27 Jan 2016 14:17:49 -0500 > Igor Tandetnik <igor at tandetnik.org> wrote: > >> On 1/27/2016 2:10 PM, Yannick Duch?ne wrote: >> > `UNIQUE` constraint allows multiple NULL: is this expected? >> >> http://www.sqlite.org/lang_createtable.html >> "For the purposes of UNIQUE constraints, NULL values are considered >> distinct from all other values, including other NULLs." >> >> I'm reasonably, but not 100%, sure this is standard-conforming. > > Thanks Igor. I overlooked it (and now feel to remember I use to know it and > was as much surprised as I am now). > > Searching the web, it seems most DB don't allow multiple `NULL` on a column > with a `UNIQUE` constraint. If the standard says any `NULL` differs from any > `NULL`, so be it and these DB are wrong. Just that now I wonder the why. >
See https://www.sqlite.org/nulls.html > Is this related to something I don't know about, named `UNKNOWN` in SQL? If > it's related, then I may understand. > > -- > Yannick Duch?ne > _______________________________________________ > sqlite-users mailing list > sqlite-users at mailinglists.sqlite.org > http://mailinglists.sqlite.org/cgi-bin/mailman/listinfo/sqlite-users > -- D. Richard Hipp drh at sqlite.org
