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Subset of a candidate key

As we know a candidate key is a column or combination of columns that uniquely identifies the rows in a relation. Suppose I have a relation in which candidate keys are combinations of columns. I want to ask, is it possible that a subset of a candidate key also uniquely identifies the row? OR is a candidate ke…

Counting related rows in a child table

I have been trying to do some queries and getting a count on related tables using eloquent. Tables: requests contact (belongs to requests) history (belongs to contact) As such X number of requests each have Y number of contacts which in term each have Z number of histories Using sql I can do something like th…