Database ----- catalog and schema introduction, ----- catalogschema

Database ----- catalog and schema introduction, ----- catalogschema

In the SQL environment, both Catalog and Schema are abstract concepts. They are mainly used to solve naming conflicts.

A database system contains multiple Catalog, and each Catalog contains multiple schemas. Each Schema contains multiple database objects (tables, views, fields, and so on)

For example, the full qualified name of the database object table can be expressed as: Catalog name. Schema name. Table Name

The SQL standard does not require that the fully qualified names of each database object be unique, just like domain names. If you like it, each IP Address can have multiple domain names.

From the perspective of implementation, the support and implementation methods for Catalog and Schema vary widely in various database systems. A simple and common implementation method is to use the database name as the Catalog name, use the username as the Schema name. For details, see the following table:

Supplier	Catalog support	Schema support
Oracle	Not Supported	Oracle User ID
MySQL	Not Supported	Database Name
Ms SQL Server	Database Name	The object owner name, which has changed since version 2005.
DB2	The Catalog part is omitted when the database object is specified.	Catalog owner name
Sybase	Database Name	Database owner name
Informix	Not Supported	No
PointBase	Not Supported	Database Name