sql(oracle)数据处理实用总结开窗函数(over partition)使用

开窗函数over partition

select test_name, test_id, n_rank, test_salary_sum
  from (select t_alias.test_name,
               t_alias.test_id,
               sum(t_alias.test_salary) test_salary_sum,
               row_number() over(partition by t_alias.test_name order by sum(t_alias.test_salary) desc) n_rank
          from (select 1 test_id, 'name_1' test_name, 100 test_salary
                  from dual
                union all
                select 2 test_id, 'name_1' test_name, 200 test_salary
                  from dual
                union all
                select 2 test_id, 'name_1' test_name, 300 test_salary
                  from dual
                union all
                select 3 test_id, 'name_1' test_name, 300 test_salary
                  from dual
                union all
                select 4 test_id, 'name_1' test_name, 400 test_salary
                  from dual
                union all
                select 1 test_id, 'name_2' test_name, 200 test_salary
                  from dual
                union all
                select 2 test_id, 'name_2' test_name, 200 test_salary
                  from dual
                union all
                select 2 test_id, 'name_2' test_name, 200 test_salary
                  from dual
                union all
                select 3 test_id, 'name_2' test_name, 400 test_salary
                  from dual
                union all
                select 4 test_id, 'name_2' test_name, 400 test_salary
                  from dual) t_alias
         group by t_alias.test_name, t_alias.test_id)
 where n_rank <= 2
 order by test_name, n_rank;

开窗函数使用于取出多列分组，取一列分组下另一组前几名，先利用开窗函数对其分组排名，开窗函数排名函数较多使用row_number()，还有rank()等，生成排名列之后将结果集筛选其排名前几<=2或者你想要的前几名。
上述执行结果：

image-the result of above example

获得每个test_name字段下test_id的test_salary的前2名。
开窗函数实例：

image-实例

另有开窗函数替代写法,可以了解：

select * from adminus;
create table adminus_test(num number(5,2),count number(5,2));
insert into adminus_test(num,count) values(1,5);
insert into adminus_test(num,count) values(1,7);
insert into adminus_test(num,count) values(1,8);
insert into adminus_test(num,count) values(2,8);
insert into adminus_test(num,count) values(2,9);
insert into adminus_test(num,count) values(2,7);
select * from adminus_test;
--开窗函数替代写法
select d.admin_id, d.num, c.count
  from (select num,
               count,
               (select count(1)
                  from adminus_test b
                 where b.num = a.num
                   and a.count <= b.count) as cnt --等级的变相的写法 --重要写法
          from adminus_test a
         group by num, count) c
  join adminus d
    on c.num = d.num
 where c.cnt <= 2;