I think Excel formulas also use this, but it’s been a long time so I might be misremembering.

Can confirm also BASICA, GWBASIC, QBASIC, and QuickBASIC

Depends on the dialect. I mostly use Presto and MySQL at work, and both allow !=.

Presto also lets you use NOT for booleans - instead of WHERE foo = false, you can do WHERE NOT foo.

If you want to be able to write practically anything on mobile, including ≠, ≈, ‰, ℝ etc., have a look at Unexpected keyboard. No spellcheck or autocomplete, though.

I was on mobile so I didn’t have a .XCompose available to type.

I feel the opposite. On mobile I have much easier access to special characters. I just need to hold down characters to get more variants.

SQL is definitely a programming language. Most dialects are Turing-complete in some way. Some allow custom functions and stored procedures.

Yes for OCaml. Haskell’s inequality is defined as /= (for ≠). <> is usually the Monoid mappend operator (i.e. generalized binary concatenation).