Add SPI to translate column types

[lukaseder]

Until recently, jOOQ's default type mappings were sufficient for most use-cases. For example, a SQL standard (and e.g. SQL Server, PostgreSQL) INT type can be mapped to Oracle NUMBER(10) on write or NUMBER(9) on read, as the latter type can include the entirety of the INT value space. Alternatively, a PostgreSQL TEXT type might be the closest equivalent to Oracle's CLOB

With the parser that was added in jOOQ 3.9, the automatic translation of types may not behave as users expect. It would be good if there was an SPI that allowed for overriding such type translations predictably.

Designing the SPI is non-trivial as it might incur quite some internal changes. Once the requirements for this SPI are more clear, this issue will be updated with more details. In particular, this SPI will need to work together with the Converter and Binding SPIs, as well as with the code generator.

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See also:

• https://groups.google.com/forum/#!topic/jooq-user/61qU8PbFBNM (MySQL VARCHAR types need a length, but the total length of a row is 64kb)