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+Each dialect has its own set of types, many of which are available only within that dialect. For example, MySQL has a `BigInteger` type and Postgres has an `Inet` type. To use these, import them from the module explicitly:
User-defined types can be created, to support either database-specific types, or customized pre-processing of query parameters as well as post-processing of result set data. You can make your own classes to perform these operations. To augment the behavior of a `TypeEngine` type, such as `String`, the `TypeDecorator` class is used:
`Unicode` and`PickleType` class es a reinstance sof `TypeDecorator` already and can be subclassed directly.
To build a type object from scratch, which will not have a corresponding database-specific implementation, subclass `TypeEngine`: