Firebird 5.0.1 introduces several bug fixes and stability improvements, as well as a noteworthy new feature for the database optimizer. The update includes the ability to convert subqueries to ANY/SOME/IN/EXISTS in semi-join operations.

This new optimization technique is disabled by default, but it has the potential to significantly improve the performance of complex SQL queries.

By converting subqueries to these more efficient constructs, the database can often execute queries faster, especially for queries involving large datasets or intricate join logic.

For a more detailed overview of all the changes and enhancements in Firebird 5.0.1, please refer to the in-depth article with detailed examples:

Firebird 5.0.1 Improvements in Optimizer