The SQL database access language remains relatively consistent between database server applications. But minor differences in the configuration and implementation of database servers can be very important to people who use them a great deal. For some high-end users, PostgreSQL is a preferable alternative to MySQL; some say that it is marginally faster, and it has different configuration options for ODBC connections. While PostgreSQL has had support for stored procedures and triggers for quite some time now, for example, MySQL will have support for these only in development versions 5.0 and beyond. PostgreSQL can also use the local authentication systems for database access (e.g., your EServer password would also be your PostgreSQL password).
As a result, we offer both MySQL and PostgreSQL to the editors of EServer collections, in addition to Gadfly (a Python-based SQL server application) and FileMaker Pro. Collection editors are free to use whatever they prefer.