|PostgreSQL Driver Notes: Details about the libdbi driver providing support for PostgreSQL backends|
This chapter lists known peculiarities of the pgsql driver. Wherever possible, nonstandard driver behavior is hidden by libdbi's abstractions, but occasionally special considerations must be taken or extra functionality may be utilized for particular drivers.
PostgreSQL has no intrinsic concept of unsigned fields (although you can still use the "OID" type as an unsigned long, or define your own user-defined unsigned types). User-defined types are not handled specially. All unrecognized datatypes are preserved as strings.
PostgreSQL does not support a 1-byte numeric datatype.