Replication of Columns Having Different Data Types
Corresponding columns on the master's and the slave's copies of the same table ideally should have
the same data type. However, beginning with MySQL 5.1.21, this is not always strictly enforced, as
long as certain conditions are met.
All other things being equal, it is always possible to replicate from a column of a given data type to
another column of the same type and same size or width, where applicable, or larger. For example,
you can replicate from a CHAR(10) column to another CHAR(10), or from a CHAR(10) column to a
CHAR(25) column without any problems. In certain cases, it also possible to replicate from a column
having one data type (on the master) to a column having a different data type (on the slave); when the
data type of the master's version of the column is promoted to a type that is the same size or larger on
the slave, this is known as attribute promotion.
Attribute promotion can be used with both statement-based and row-based replication, and is not
dependent on the storage engine used by either the master or the slave. However, the choice of
logging format does have an effect on the type conversions that are permitted; the particulars are
discussed later in this section.
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