n is either 1 or 0. The default value is 1.
When FastDistinct is enabled (n = 1), SQL queries involving DISTINCT or GROUP BY clauses run more efficiently by making better use of indices (if indices are available).
The values returned by such queries are collated in the same way they are stored within the index. This means the results of such queries may be all uppercase. This may have an effect on case-sensitive applications.
Changing This Parameter
FastDistinct is enabled by default. On the SQL page of the Management Portal (System Administration > Configuration > SQL and Object Settings > SQL), select GROUP BY and DISTINCT queries must produce original values to disable FastDistinct.
You can also change FastDistinct with the Config.SQL class (as described in the class reference) or by editing the CPF in a text editor (as described in the Editing the Active CPF section of the “Introduction to the Configuration Parameter File” chapter in this book).