MDEV-22758 Assertion `!item->null_value' failed in Type_handler_inet6::make_sort_key_part

When some expression of an INET6 data type involves conversion to INET6 from
other data types, e.g. in:

- CAST:

    SELECT CAST(non_inet6_expr AS INET6)

- CASE and hybrid functions:

    SELECT CASE WHEN expr THEN inet6_expr ELSE non_inet6_expr END

- UNION:

    SELECT inet6_expr UNION SELECT non_inet6_expr

the result column must be fixed as NULL-able even if the non-inet6 expression itself
is not NULL-able, because at the execution time the conversion can fail.

Details:
- Forcing NULL-ability if conversion from some data type to INET6 is involved
  (for non-constant or for expensive expressions).
- Non-expensive constant expressions are tested for NULL-ability at fix_fields() time,
  so things like `CAST('::' AS INET6)` are still detected as NOT NULL.
- Adding "bool warn" parameter into a few methods, to avoid redundant warnings
  at fix_fields() time when calculating NULL-ability of constant values.

0 files changed, 0 insertions, 0 deletions