oracle中交集，并集，差集详解

/* union/union all运算：返回两个结果集的并集，即将两个查询的结果集进行合并。
   union all：不过滤重复数据。
   union：过滤重复数据
*/
select name from driver_info where firm_id = "0"
union all
select name from driver_info where firm_id = "914";

select name from driver_info where firm_id = "0"
union
select name from driver_info where firm_id = "914";

/* intersect运算：返回两个结果集的交集，即取两个结果集中相同的部分。会过滤重复结果集*/
select name from driver_info where firm_id = "0"
intersect
select name from driver_info where firm_id = "914";

/* minus运算：返回第一个结果集与第二个结果集中不相同的部分数据。*/
select name from driver_info where firm_id = "0"
minus
select name from driver_info where firm_id = "914";