MySQL表达式之公用表表达式(CTE)的使用示例

示例一

数据表中有每个企业每年每月并且每月的产值是累加的数据的数据记录

• 需求：

统计企业产值能力，找出所有家企业中产值最高的企业，其产值记为P。对于第i家企业，其产值为Pi则该企业的产值能力评分=Pi/P×100。

• SQL：

--        使用ROW_NUMBER()为每个企业每年每个月的产值排名，筛选出每个企业每年最大月份的产值。
        WITH MaxMonthlyOutput AS (SELECT company_id,
                                         declare_year,
                                         declare_month,
                                         total_industrial_value,
                                         ROW_NUMBER() OVER (PARTITION BY company_id, declare_year ORDER BY declare_month DESC) as rn
                                  FROM company_revenue_info),
--             从MaxMonthlyOutput中筛选出每个企业每年最大月份的产值。
             MaxYearlyOutput AS (SELECT company_id,
                                        declare_year,
                                        total_industrial_value
                                 FROM MaxMonthlyOutput
                                 WHERE rn = 1),
--             计算每个企业每年的最大月份产值的总和，得到Pi。
             SumYearlyOutput AS (SELECT company_id,
                                        SUM(total_industrial_value) as Pi
                                 FROM MaxYearlyOutput
                                 GROUP BY company_id),
--              找出所有企业的Pi中的最大值，记为P。
             MaxPi AS (SELECT MAX(Pi) as P
                       FROM SumYearlyOutput)
--            计算每个企业的得分，公式为Pi/P*100。
        SELECT syo.company_id         AS companyId,
               syo.Pi                 AS perValue,
               mpa.P                  AS standardValue,
               (syo.Pi / mpa.P * 100) AS score
        FROM SumYearlyOutput syo
                 CROSS JOIN
             MaxPi mpa;

• MySQL5兼容语法

SELECT 
    s.company_id AS companyId,
    COALESCE(s.Pi, 0) AS perValue,  -- 空值转0
    COALESCE(m.P, 1) AS standardValue,  -- 防止除零错误
    ROUND(
        (COALESCE(s.Pi, 0) / NULLIF(COALESCE(m.P, 1), 0) * 100), 
        4
    ) AS score
FROM 
    (SELECT 
        company_id,
        COALESCE(SUM(total_industrial_value), 0) AS Pi  -- 子查询空值处理
     FROM 
        (SELECT r.company_id, r.total_industrial_value
         FROM company_revenue_info r
              INNER JOIN 
              (SELECT company_id, declare_year, MAX(declare_month) AS max_month
               FROM company_revenue_info
               GROUP BY company_id, declare_year) m
              ON r.company_id = m.company_id 
                 AND r.declare_year = m.declare_year 
                 AND r.declare_month = m.max_month) sub
     GROUP BY company_id) s
CROSS JOIN 
    (SELECT COALESCE(MAX(Pi), 1) AS P  -- 确保标准值不为NULL
     FROM 
        (SELECT COALESCE(SUM(total_industrial_value), 0) AS Pi
         FROM 
             (SELECT r.company_id, r.total_industrial_value
              FROM company_revenue_info r
                   INNER JOIN 
                   (SELECT company_id, declare_year, MAX(declare_month)