How Do Database Concepts Like Catalogs, Schemas, Users, and Instances Differ Across Vendors?

Catalogs, Schemas, Users, and Database Instances: A Comparative Analysis

When comparing databases across different vendors, it is critical to understand the relationship between these fundamental concepts: catalogs, schemas, users, and database instances.

Unique Object Identification

To uniquely identify an object in a database, the required parameters vary depending on the implementation. In Oracle, a combination of schema name and object name is sufficient. In PostgreSQL, the database name must also be specified. In MySQL, only the database name is needed.

Catalog as an Abstraction

A catalog is essentially an abstraction of data storage. It acts as a self-contained isolated namespace, but not all SQL engines adhere to this definition.

Database and Schema

The concepts of database and schema are relatively consistent across vendors. A database represents a namespace qualifier within a server, while a schema is a namespace within a database that typically associates with access control layer.

User and Ownership

A user is a named account that grants access to one or more databases. In Oracle, a user is identical to a schema owner. In PostgreSQL, users can own schemas and objects within each allowed database separately. In MySQL, users cannot own objects but have access to one or more databases.

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