The SQL used to manage dates and times varies by database type. The code to generate this SQL (e.g.,
FROM_UNIXTIME()) has historically been handled by modules that work with dates and times, wrapped in long switch statements to handle the officially supported databases. (more or less.) A d.o issue raised the possibility of a date abstraction API, but nothing ever came of it.
Similar to #2888, this is code that was created to support PostgreSQL in Silkscreen and is submitted here because the non-PostgreSQL part of the patch is valid for Backdrop, even if all it accomplishes is better encapsulation of database code in the database classes.
Unlike #2888 and #2889, this is a little more invasive, changing the
date_sql_handler class in the Date module, and several Views handlers.
As with #2888, I'm submitting this because I consider it good open source etiquette to provide patches to parent projects, even if the patch's true purpose cannot be realized upstream, in this case database independence.