"It is elementary that 'The doctrine of res judicata gives certain conclusive effect to a former judgment in subsequent litigation involving the same controversy. It seeks to curtail multiple litigation causing vexation and expense to the parties and wasted effort and expense in judicial administration.' " ( Nakash v. Superior Court (1987) 196 Cal. App. 3d 59, 67 [241 Cal. Rptr. 578], quoting 7 Witkin, Cal. Procedure (3d ed. 1985) Judgment 188, p. 621, italics omitted.) Generally speaking, a valid final judgment in favor of a plaintiff merges any claim of the same cause of action in the judgment, and precludes the plaintiff from maintaining any later suit on the same cause of action. (Hatch v. Bank of America (1960) 182 Cal. App. 2d 206, 210-211 [5 Cal. Rptr. 875].) This aspect of res judicata applies to judgments rendered by the small claims court. (Perez v. City of San Bruno (1980) 27 Cal. 3d 875, 884 [168 Cal. Rptr. 114, 616 P.2d 1287]; Sanderson v. Niemann (1941) 17 Cal. 2d 563, 573 [110 P.2d 1025].) The rule against a plaintiff splitting a single cause of action so as to make it the basis of several suits is, in part, an application of the doctrine of res judicata. ( People v. Damon (1996) 51 Cal. App. 4th 958, 974 [59 Cal. Rptr. 2d 504]; Boccardo v. Safeway Stores, Inc. (1982) 134 Cal. App. 3d 1037, 1043 [184 Cal. Rptr. 903]; Ferraro v. Southern Cal. Gas Co. (1980) 102 Cal. App. 3d 33, 41 [162 Cal. Rptr. 238].) In determining whether a cause of action has been split, the relief sought by the injured party should not be confused with the cause of action; "The violation of one primary right constitutes a single cause of action, though it may entitle the injured party to many forms of relief . . . ." ( Wulfjen v. Dolton (1944) 24 Cal. 2d 891, 895-896 [151 P.2d 846]; accord, People v. Damon, supra, at p. 974.)