The columns of the information schema views use special data types that are defined in the information schema. These are defined as simple domains over ordinary built-in types. You should not use these types for work outside the information schema, but your applications must be prepared for them if they select from the information schema.
These types are:
cardinal_numberA nonnegative integer.
character_dataA character string (without specific maximum length).
sql_identifier
A character string. This type is used for SQL identifiers, the
type character_data is used for any other kind of
text data.
time_stamp
A domain over the type timestamp with time zone
yes_or_no
A character string domain that contains
either YES or NO. This
is used to represent Boolean (true/false) data in the
information schema. (The information schema was invented
before the type boolean was added to the SQL
standard, so this convention is necessary to keep the
information schema backward compatible.)
Every column in the information schema has one of these five types.