Informationschema

Information_schema is a standardized, read‑only collection of views that expose metadata about objects in a relational database management system. It is implemented as a dedicated schema or database named information_schema and provides a portable interface to information such as schemas, tables, columns, constraints, routines, privileges, and data types. The exact set of views and their contents vary by vendor, but common views include information_schema.tables, information_schema.columns, information_schema.schemata, information_schema.table_constraints, information_schema.key_column_usage, information_schema.routines, and information_schema.columns_privileges.

The information_schema serves as a stable, cross‑vendor means of discovering database structure. It is particularly useful for applications that need to adapt to different systems, for tooling, and for tasks such as dynamic SQL generation or schema introspection. Typical queries extract details like which tables exist in a schema, the data types of columns, or the constraints applied to tables. For example, queries can retrieve base tables in a given schema or list column data types across tables.

Access to information_schema is usually read‑only; metadata is exposed rather than modifiable through these views. Visibility is subject to user privileges, so users may see only objects they have permission to access. Some metadata may be incomplete or vendor‑specific, reflecting differences in implementations and coverage across systems.

In practice, information_schema is supported by several major DBMS products (such as MySQL, PostgreSQL, and SQL Server) and is valued for portability. Oracle and other systems provide their own data dictionary or catalog views, offering similar metadata access, while information_schema support may vary or be complemented by vendor‑specific views.