SET RELATION TO [eExpression1 INTO nWorkArea1 | cTableAlias1 [, eExpression2 INTO nWorkArea2 | cTableAlias2 ...] [IN nWorkArea | cTableAlias] [ADDITIVE]]Also SET RELATION TO on its own clears all relations. However it doesn't appear to work with the IN clause.
SET RELATION [IN nWorkArea | cTableAlias] TO [eExpression1 INTO nWorkArea1 | cTableAlias1 [, eExpression2 INTO nWorkArea2 | cTableAlias2 ...] [ADDITIVE]]