在不使用解析函数的情况下实现 Rank

Question

我想知道是否有一种方法可以在不使用内置函数的情况下实现 SQL 分析函数。

SELECT *,
    ROW_NUMBER() OVER (PARTITION BY dept_id ORDER BY salary DESC) AS rownum,
    DENSE_RANK() OVER (PARTITION BY dept_id ORDER BY salary DESC) AS denserank,
    RANK() OVER (PARTITION BY dept_id ORDER BY salary DESC) AS rnk
FROM emp;

Answer 1

您可以使用相关的子查询来做到这一点。

select dept_id,salary,
(select count(*) from emp e1 where e1.dept_id=e.dept_id and e1.salary>=e.salary) as rnum
from emp e

当没有关系时，这很有效。

Answer 2

下面是三个等价的表达式：

select emp.*,
       (select count(*)
        from emp emp2
        where emp2.dept_id = emp.dept_id and
              (emp2.salary > emp.salary or
               emp2.salary = emp.salary and emp2.emp_id <= emp.emp_id
              )
       ) as "row_number",
       (select 1 + count(*)
        from emp emp2
        where emp2.dept_id = emp.dept_id and
              emp2.salary > emp.salary 
              )
       ) as "rank",
       (select count(distinct salary)
        from emp emp2
        where emp2.dept_id = emp.dept_id and
              emp2.salary >= emp.salary
       ) as "dense_rank",
from emp;

这假定存在 emp_id 以使行对 "row_number" 唯一。

Answer 3

这适用于所有情况

select DEPT_ID, SALARY,

    (select count(*)+1  from emp r where r.SALARY>o.SALARY and r.dept_id=o.dept_id) **rank**,

    (select count(distinct SALARY )+1  from emp r where r.SALARY>o.SALARY and r.dept_id=o.dept_id) *d_rank*,

    (select count(*)+1  from (select x.*,rownum rn from ( select emp.* from emp  order by DEPT_ID asc,salary desc ) x) r where r.rn<o.rn and r.dept_id=o.dept_id) **rownumm**

from (select x.*,rownum rn from ( select emp.* from emp  order by DEPT_ID asc,salary desc ) x) o 

order by DEPT_ID,salary desc;

对于排名：- 使用（（小于当前行的值的计数）+1

计算

对于密集排名：- 与排名相同（计数小于当前行的不同值）+1

row_number：- 通过为每一行生成 rownum 来创建嵌套查询，这对于所有行都是不同的。现在最重要的是执行与排名相同的逻辑（大于前一个行数的值计数（select 子查询的行数））+1

在不使用解析函数的情况下实现 Rank

Implement Rank without using analytic function

sql

ansi-sql