The length of variable length columns that are part of any index, including primary and unique keys, defined when the registry variable DB2_INDEX_2BYTEVARLEN was on, can be altered to a length greater than 255 bytes. The fact that a variable length column is involved in a foreign key will no longer prevent the length of that column from being altered to larger than 255 bytes, regardless of the registry variable setting. However, data with length greater than 255 cannot be inserted into the table unless the column in the corresponding primary key has length greater than 255 bytes, which is only possible if the primary key was created with the registry variable ON.
Indexes can be defined on variable length columns whose length is greater than 255 bytes if the registry variable DB2_INDEX_2BYTEVARLEN is ON.
Primary and unique keys with variable keyparts can have a size greater than 255 if the registry variable DB2_INDEX_2BYTEVARLEN is ON. Foreign keys can be defined on variable length columns whose length is greater than 255 bytes.