After reading it, this is not a duplicate of Explicit vs Implicit SQL Joins. The answer may be related (or even the same) but the question is diffe
Normally, filtering is processed in the WHERE clause once the two tables have already been joined. It’s possible, though that you might want to filter one or both of the tables before joining them. i.e, the where clause applies to the whole result set whereas the on clause only applies to the join in question.