Comparison of relational database management systems

Note (1):
The following tables compare general and technical information for a number of relational database management systems.wikipedia
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Percona Server for MySQL

Percona Server
* Comparison of relational database management systems

IBM Informix

MySQL

M'''ySQLMySQL 4.1MySQL 4.x
The problem that arises is that former MySQL users will create multiple databases for one project.

PostgreSQL

PostgresPgSQLPgAdmin
Conversely, PostgreSQL has applied more of the specification implementing cross-table, cross-schema, and then left room for future cross-database functionality.

SQL

Structured Query LanguageSQL databaseSQL Databases
The SQL specification defines what an "SQL schema" is; however, databases implement it differently.