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_number
A nonnegative integer.
character_data
A 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
Every column in the information schema has one of these four types.
Boolean (true/false) data is represented in the information schema
by a column of type character_data
that contains
either YES
or NO
. (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.)