Information schema


In relational databases, the information schema is an ANSI-standard set of read-only views that provide information about all of the tables, views, columns, and procedures in a database. It can be used as a source of the information that some databases make available through non-standard commands, such as:
=> SELECT count FROM information_schema.tables;
count
-------
99

=> SELECT column_name, data_type, column_default, is_nullable
FROM information_schema.columns WHERE table_name='alpha';
column_name | data_type | column_default | is_nullable
-------------+-----------+----------------+-------------
foo | integer | | YES
bar | character | | YES

=> SELECT * FROM information_schema.information_schema_catalog_name;
catalog_name
--------------
johnd

Implementation

As a notable exception among major database systems, Oracle does not implement the information schema. An exists to address this.
RDBMSs that support information_schema include:
RDBMSs that do not support information_schema include: