minus，union，union all，intersect 这几个的区别和用法

/*minus:只取不重复的记录*/
   select count(1) into vn_count
                   from (select t.*, t.rowid from emp t
                   minus
                   select s.*, s.rowid from emp s);
   dbms_output.put_line('minus rows in table emp is:' || vn_count);   
              
/*union: 取两个查询记录（去掉重复的）**/
   select count(1)  into vn_count
                    from (select t.*, t.rowid from emp t
                    union
                    select s.*, s.rowid from emp s);
   dbms_output.put_line('union rows in table emp is:' || vn_count);   
                   
/*union all: 取两个查询所有的记录（包括重复的）**/
   select count(1) into vn_count
                     from (select t.*, t.rowid from emp t
                     union all
                     select s.*, s.rowid from emp s);
  dbms_output.put_line('union all rows in table emp is:' || vn_count);     
                     
/*intersect: 只取重复的记录（相当于交集吧）*/   
   select count(1)into vn_count
                      from (select t.*, t.rowid from emp t
                      intersect
                      select s.*, s.rowid from emp s);

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