The query is simply very badly written. Who makes a left join of a 5b rows table to a smaller table and at the same time expects a distinct from the “left” tabl

The query is simply very badly written. Who makes a left join of a 5b rows table to a smaller table and at the same time expects a distinct from the “left” table??? If the distinct is important to solve the problem without expecting the join to return “true” then why have a join at first place???