In discussing, first, the joinder of actions it will be convenient to consider three groups or classes of cases:

Class I : Where one plaintiff (or joint plaintiffs) unites in a single proceeding two or more causes of action against one defendant (or joint defendants).

Class 2: "Where two or more plaintiffs, each having a cause of action against the same party (or parties), unite their causes of action in one proceeding.

Class 3: Where one plaintiff (or joint plaintiffs) having several causes of action, each against a different party, unites them in one proceeding.

In considering each group or class of cases two situations should be noticed: (a) Where the causes sought to be joined are entirely separate and distinct, and (b) where they present common questions of law or fact.