Type Definition diesel::
pub type LeftJoinQuerySource<Left, Right, On = <Left as JoinTo<Right>>::OnClause> = JoinOn<Join<Left, Right, LeftOuter>, On>;
A query source representing the left outer join between two tables.
For example, for the left join between three tables that implement
LeftJoinQuerySource<LeftJoinQuerySource<table1, table2>, table3>
Which conveniently lets you omit the exact join condition.