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In relational databases, the information schema (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
SHOWcommand of MySQL - the
DESCRIBEcommand of Oracle's SQL*Plus - the
\dcommand in psql (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)
Video Information schema
Implementation
As a notable exception among major database systems, Oracle does not as of 2015 implement the information schema. An open-source project exists to address this.
RDBMSs which support information_schema include:
- Microsoft SQL Server
- MySQL
- PostgreSQL
- InterSystems Caché
- H2 Database
- HSQLDB
- MariaDB
RDBMSs which do not support information_schema include:
- Oracle Database
- IBM DB2
- SQLite
- Sybase ASE
Maps Information schema
See also
- Oracle metadata
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External links
- Information schema in H2 Database
- 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
- Information Schema in MariaDB
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References
Source of article : Wikipedia
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