insert into A (col_a) sel null as col_a from B; *** Failure 5407 Invalid operation on an ANSI Datetime or Interval value.
The problem is that, in standard SQL, NULL is not a general value expression. NULL is a special syntactical element that is allowed only in certain specified contexts. The correct solution is to use CAST, like this:
insert into A (col_a) sel cast(null as time(6)) from b; *** Insert completed. No rows added.