Inrelational databases, theinformation schema (information_schema) is anANSI-standard set of read-only views that provide information about all of thetables,views,columns, andprocedures in a database.[1] It can be used as a source of the information that some databases make available through non-standard commands, such as:
SHOW command ofMySQLDESCRIBE command ofOracle'sSQL*Plus\d command inpsql (PostgreSQL's default command-line program).=> SELECT count(table_name) FROM information_schema.tables; count ------- 99 (1 row) => 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 (2 rows) => SELECT * FROM information_schema.information_schema_catalog_name; catalog_name -------------- johnd (1 row)
As a notable exception among major database systems, Oracle does not as of 2015[update] implement the information schema. Anopen-source project exists to address this.
RDBMSs that support information_schema include:
RDBMSs that do not support information_schema include:
Metadata that applies primarily to the runtime database environment is managed through the INFORMATION_SCHEMA. [...] Metadata that applies to the information system environment as a whole is managed through the dictionary or repository.
