If we have the filter expression "WHERE m[?] = 2", the existing code
simply assumed that the subscript is an object of the right type.
However, while it should indeed be the right type (we already have code
that verifies that), there are two more options: It can also be a NULL,
or an UNSET_VALUE. Either of these cases causes the existing code to
dereference a non-object as an object, leading to bizarre errors (as
in issue #10361) or even crashes (as in issue #10399).
Cassandra returns a invalid request error in these cases: "Unsupported
unset map key for column m" or "Unsupported null map key for column m".
We decided to do things differently:
* For NULL, we consider m[NULL] to result in NULL - instead of an error.
This behavior is more consistent with other expressions that contain
null - for example NULL[2] and NULL<2 both result in NULL as well.
Moreover, if in the future we allow more complex expressions, such
as m[a] (where a is a column), we can find the subscript to be null
for some rows and non-null for other rows - and throwing an "invalid
query" in the middle of the filtering doesn't make sense.
* For UNSET_VALUE, we do consider this an error like Cassandra, and use
the same error message as Cassandra. However, the current implementation
checks for this error only when the expression is evaluated - not
before. It means that if the scan is empty before the filtering, the
error will not be reported and we'll silently return an empty result
set. We currently consider this ok, but we can also change this in the
future by binding the expression only once (today we do it on every
evaluation) and validating it once after this binding.
Fixes#10361Fixes#10399
Signed-off-by: Nadav Har'El <nyh@scylladb.com>
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