Incompatible Change: For BINARY columns, the pad value and how it is handled has changed. The pad value for inserts now is 0x00 rather than space, and there is no stripping of the pad value for selects. For details, see The BINARY and VARBINARY Types.

Incompatible Change: The CHAR() function now returns a binary string rather than a string in the connection character set. An optional USING charset clause may be used to produce a result in a specific character set instead. Also, arguments larger than 256 produce multiple characters. They are no longer interpreted modulo 256 to produce a single character each. These changes may cause some incompatibilities, as noted in Upgrading from MySQL 4.0 to 4.1.