The following methods:
use methods cmp_type() and result_type() of their arguments.
The is not friendly to pluggable data types.
Pluggable data types should be able to define their own fix_length_and_dec() logic.
Under term of this task we'll split implementations of these methods into new methods in Type_handler:
We'll also make the server return an error when a GOMETRY type expression appears as an argument of the affected operations.