Refactor DB query functions

[Macroz]

Refactor DB query functions which could have a "search" function with 0..n and singular "get" function with 0..n and return :1.

-- :name get-application-events :? :*
-- :name get-application-event :? :*

Former should be a "search" that can return many, and has filters. The latter should always return at most one result, and not a sequence.

Consider writing an ADR about the conventions.