Function sql::plan::lowering::attempt_outer_join

fn attempt_outer_join(
    left: MirRelationExpr, 
    right: MirRelationExpr, 
    on: MirScalarExpr, 
    kind: JoinKind, 
    oa: usize, 
    id_gen: &mut IdGen
) -> Option<MirRelationExpr>

Attempts an efficient outer join, if on has equijoin structure.