The code in Type_handler_blob****::make_conversion_table_field()
erroneously assumed that row format replication uses
MYSQL_TYPE_TINYBLOB, MYSQL_TYPE_BLOB, MYSQL_TYPE_MEDIUMBLOB,
MYSQL_TYPE_LONGBLOB type codes to tranfer BLOB variations.
In fact, all BLOB variations use MYSQL_TYPE_BLOB as the type
code, while the BLOB packlength (1,2,3 or 4) it tranferred
in metadata.
The bug was introduced by aee068085ddb13f700780eeb61fce29c1e37df63
(MDEV-9238 Wrap create_virtual_tmp_table() into a class, split into different steps)
Item_func_hybrid_field_type did not return correct field_type(), cmp_type()
and result_type() in some cases, because cached_result_type and
cached_field_type were set in independent pieces of the code and
did not properly match to each other.
Fix:
- Removing Item_func_hybrid_result_type
- Deriving Item_func_hybrid_field_type directly from Item_func
- Introducing a new class Type_handler which guarantees that
field_type(), cmp_type() and result_type() are always properly synchronized
and using the new class in Item_func_hybrid_field_type.
