PostgreSQL 8.4.21 Documentation
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# 33.2. Data Types

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.)

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