# Limitations and considerations

The following limitations apply:

* When replicating to the MariaDB target database, if the DATETIME value is set to zero, you need to define a transformation that replaces the DATETIME with valid values. For example:

  `replace($datetime_column,'9999-12-31 23:59:59','2000-01-01 22:00:00')`

* Due to the way MySQL operates, when loading data to a MySQL target during a Full Load task, duplicate key errors will not be reported to the logs.

* When updating a column's value to its existing value, a zero rows affected is returned from MySQL (unlike Oracle and Microsoft SQL Server that perform an update of one row).

  This generates an entry in the `attrep_apply_exceptions Control Table` and the following warning:

  ` Some changes from the source database had no impact when applied to the target database. See attrep_apply_exceptions table for details.  `

* If you need to replicate 4-byte emoji characters, the target schema character set must be set to utf8mb4.