Honestly, if Latin-speakers had invented high-level programming languages (and, especially, languages intended for the kind of use and audience that motivated the design of SQL), they'd probably just include noun declensions as part of the declaration, and then decline the noun properly for the way they were used, rather than settling on single form.

Yes, that's not something we'd do with Latin declensions in a language designed by English speakers, but that isn't really an argument against naming collections with plural nouns in such a language, just because doing what might be natural in a language designed by Latin speakers to resemble Latin doesn't make sense to us.