In relational databases, the information schema is an ANSI standard set of read-only views which provide information about all of the tables, views, columns, and procedures in a database. It can be used as a source of the information which some databases make available through non-standard commands, such as the
SHOW command of MySQL, the
DESCRIBE command of Oracle, and the
\d command in psql (PostgreSQL's default terminal).
=> 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 currently implement the information schema. There is an open source project trying to make up for that.
- Information schema in MySQL 5.7
- Information schema in PostgreSQL (current version)
- Information schema in SQLite
- Information schema in Microsoft SQL Server 2014
- Information schema in Microsoft SQL Server Compact 4.0
- Oracle Information Schema project on sourceforge
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