Oacle SQL：命令执行不正常

Question

我正在oracle SQL developer

中执行以下查询

SELECT PROPERTYNO FROM VIEWING WHERE COMMENTS IS NOT NULL
UNION (SELECT PROPERTYNO FROM PROPERTYFORRENT MINUS SELECT PROPERTYNO FROM VIEWING);

但我收到了以下错误，但我觉得我的查询是正确的。任何人都可以建议我查询中的错误吗？

SELECT PROPERTYNO FROM VIEWING WHERE COMMENTS IS NOT NULL
UNION (SELECT PROPERTYNO FROM PROPERTYFORRENT MINUS SELECT PROPERTYNO FROM VIEWING)
Error report -
ORA-00933: SQL command not properly ended
00933. 00000 -  "SQL command not properly ended"
*Cause:    
*Action: