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.