Hello SQL Experts,
Can I purchase SQL 2019 and downgrade to 2016?
The reason for that is because we do have an application that is supported only by the 2016 version.
If so, is there a downtime when tables are indexed during maintenance?
How much would assurance cost?
The other q, "is there a downtime when tables are indexed during maintenance", is a totally different subject. Generally yes, but it could depend on the specific edition of SQL you licensed (Enterprise has many more tools for avoiding down time while doing maintenance.)
note also that you can have several versions of SQL used by different instances of SQL:
So the Admin interface can be SQL 2019, and one of the instance running with SQL 2016.