Re: Why does jsonb_set() remove non-mentioned keys?

Aha! I had mis-understood how "strict"-ness works.

Thank you David for the explanation!

Thomas: the two main pieces are these:

> SQL null and json null are represented differently

As far as SQL is concerned, `'null'::jsonb` is a valid (non-`NULL`)
value. The SQL part of Postgres doesn't "look inside" the jsonb value,
the same way it doesn't "look inside" numbers or strings or
whatever. It only cares if they're `NULL` or not, and then it passes
them to functions and operators (ok, it does look at boolean values
for `WHERE` clauses, but even `ORDER BY` is handled by comparison
operators)

> strict functions with sql null inputs yield sql null output without
> even executing the function

So when the SQL-level executor sees a call to any function declared
strict with some NULL parameters, it doesn't call the function at
all. `whatever_my_function('a string',1234,NULL)` is always `NULL`

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