SQL KEEP 窗口函数等价改写案例

一哥们出条sql题给我玩,将下面sql改成不使用keep分析函数的写法。

复制代码
select deptno,
       ename,
       sal,
       hiredate,
       min(sal) keep(dense_rank first order by hiredate) over(partition by deptno) min_sal,
       max(sal) keep(dense_rank last order by hiredate) over(partition by deptno) max_sal
  from emp;

我一开始改错了,被这哥们喷菜鸡,我草。

复制代码
-- 错误等价改写,逻辑不等价
with x as (
select e1.deptno,
       e1.ename,
       e1.sal,
       e1.hiredate,
       row_number() over (partition by DEPTNO order by HIREDATE) rn_first,
       row_number() over (partition by DEPTNO order by HIREDATE DESC) rn_last
from EMP e1)
select
    e.deptno,
    e.ename,
    e.sal,
    e.hiredate,
    x1.SAL,
    x2.SAL
from emp e
    inner join x x1 on e.DEPTNO = x1.DEPTNO and x1.rn_first = 1
    inner join x x2 on e.DEPTNO = x2.DEPTNO and x2.rn_last = 1;

我换了张表测试下,发现上面改写是逻辑有问题,如果同一个组内有相同日期的分组字段内有NULL值的,确实会导致SQL结果集不一致。

复制代码
-- 将EMP表替换成EMPLOYEES,如果使用上面等价改写就错误了。
select DEPARTMENT_ID,
       FIRST_NAME,
       SALARY,
       HIRE_DATE,
       min(SALARY) keep(dense_rank first order by HIRE_DATE) over(partition by DEPARTMENT_ID) min_sal,
       max(SALARY) keep(dense_rank last order by HIRE_DATE) over(partition by DEPARTMENT_ID) max_sal
from EMPLOYEES;

最终等价改写的SQL,增加了分组字段内有NULL值的逻辑和处理一个组内有相同日期的逻辑。

复制代码
select e.DEPARTMENT_ID,
       e.FIRST_NAME,
       e.SALARY,
       e.HIRE_DATE,
       (select MIN_SALARY
        from (select DEPARTMENT_ID, MIN(SALARY) MIN_SALARY
              from (select DEPARTMENT_ID,
                           SALARY,
                           HIRE_DATE,
                           dense_rank() over (PARTITION BY DEPARTMENT_ID ORDER BY HIRE_DATE) RN
                    from EMPLOYEES)
              WHERE RN = 1
              GROUP BY DEPARTMENT_ID) e1
        where case when e1.DEPARTMENT_ID is null then 99999 else e1.DEPARTMENT_ID end = case when e.DEPARTMENT_ID is null then 99999 else e.DEPARTMENT_ID end) a_min,
       (select MAX_SALARY
        from (select DEPARTMENT_ID, MAX(SALARY) MAX_SALARY
              from (select DEPARTMENT_ID,
                           SALARY,
                           HIRE_DATE,
                           dense_rank() over (PARTITION BY DEPARTMENT_ID ORDER BY HIRE_DATE DESC) RN
                    from EMPLOYEES)
              WHERE RN = 1
              GROUP BY DEPARTMENT_ID) e1
        where case when e1.DEPARTMENT_ID is null then 99999 else e1.DEPARTMENT_ID end = case when e.DEPARTMENT_ID is null then 99999 else e.DEPARTMENT_ID end ) a_max
FROM EMPLOYEES e;

差集比较后是等价的:

相关推荐
scheduleTTe8 小时前
SQL增查
数据库·sql
SoFlu软件机器人17 小时前
告别手动报表开发!描述数据维度,AI 自动生成 SQL 查询 + Java 导出接口
java·数据库·sql
云边散步21 小时前
🥢 第2篇:SELECT就是点菜,FROM就是菜单 —— 写你人生第一句SQL!
sql·mysql
收获不止数据库1 天前
技术人生——第13集:回归本源,大道至“减”
数据库·人工智能·职场和发展·数据库开发·sql优化·数据库优化·数据库设计
见未见过的风景1 天前
想删除表中重复数据,只留下一条,sql怎么写
数据库·sql
hello 早上好2 天前
MyBatis 动态 SQL、#{}与 ${}区别、与 Hibernate区别、延迟加载、优势、XML映射关系
sql·mybatis·hibernate
NullPointerExpection2 天前
LLM大语言模型不适合统计算数,可以让大模型根据数据自己建表、插入数据、编写查询sql统计
数据库·人工智能·sql·算法·llm·llama·工作流
我命由我123452 天前
Spring Boot - Spring Boot 集成 MyBatis 分页实现 手写 SQL 分页
java·spring boot·后端·sql·spring·java-ee·mybatis
切糕师学AI2 天前
SQL中对字符串字段模糊查询(LIKE)的索引命中情况
数据库·sql
茅坑的小石头2 天前
SQL,在join中,on和where的区别
sql