使用UNIOn子句进行选择

使用UNIOn子句进行选择

您应该使用

INTERSECT

和

MINUS

（对于Oracle）：

-- At least at Boston or at Dallas (SELECt DNAME    FROM DEPARTMENT   WHERe CITY = 'DALLAS'UNIOn SELECt DNAME    FROM DEPARTMENT   WHERe CITY = 'BOSTON')MINUS-- At Boston and at Dallas(SELECt DNAME    FROM DEPARTMENT   WHERe CITY = 'DALLAS'INTERSECT SELECt DNAME    FROM DEPARTMENT   WHERe CITY = 'BOSTON')

由于

UNIOn

添加 子查询，而

EXCEPT

/

MINUS

减去 它们