Information schema

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.^[1] 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's SQL*Plus
• the \d command 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)

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
• MariaDB

RDBMSs which do not support information_schema include:

• Oracle Database
• IBM DB2
• SQLite

See also

• Oracle metadata

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

References