The following tables compare general and technical information for a number of relational database management systems.
Unless otherwise specified in footnotes, comparisons are based on the stable versions without any add-ons, extensions or external programs.
The following is pseudo code: The problem that arises is that former MySQL users will create multiple databases for one project.
Conversely, PostgreSQL has applied more of the specification implementing cross-table, cross-schema, and then left room for future cross-database functionality.
In summary, PostgreSQL fully supports schemas and multi-tenancy by strictly separating databases from each other and thus lacks some functionality MySQL has with databases, while MySQL does not even attempt to support standard schemas.
With the 'shared-everything' Oracle RAC architecture, the same database can be opened by multiple servers concurrently.
[188] While support for ISO/IEC 9075-9 bridges the gap between the two competing philosophies surrounding schemas, MySQL and Informix maintain an implicit association between databases while ISO/IEC 9075-9 requires that any such linkages be explicit in nature.