计数，拥有和案例陈述

Posted 2023-03-23

【中文标题】计数，拥有和案例陈述

【英文标题】：Count, Having and Case statement

【发布时间】：2013-09-25 16:49:17

【问题描述】：

我希望根据 3 个不同的条件（DB2 数据库）生成项目计数。我需要计算所有项目 = .5 和 >= 1.00 (percentage_used)，但只能按 dim_building_id 和 building_name 分组。当然，这个查询不会运行，因为它需要将 percent_used 添加到 group by。如何使用 percent_used 处理这 3 个条件？

SELECT
SUM(CAST(FTS.GROUP_A AS BIGINT)) AS GROUP_A,
        SUM(CAST(FTS.GROUP_B AS BIGINT)) AS GROUP_B,
        SUM(CAST(FTS.GROUP_C AS BIGINT)) AS GROUP_C,


                CASE WHEN FAT.PERCENTAGE_USED <= '0.10'
                THEN COUNT(*)
                END AS PROJECTS_L10,
                CASE WHEN FAT.PERCENTAGE_USED >= '0.50' 
                THEN COUNT(*)
                END AS PROJECTS_G50,
                CASE WHEN FAT.PERCENTAGE_USED >= '1.00' 
                THEN COUNT(*)
                END AS PROJECTS_G100,
        DAYS(DATE('2014-07-01')) - DAYS(CURRENT DATE)  AS DAYS_LEFT,
        (DAYS(DATE('2014-07-01')) - DAYS(CURRENT DATE))/7 AS WEEKS_LEFT, 
        DAYS(DATE('2013-12-31')) - DAYS(CURRENT DATE) AS DAYS_LEFT_YEAR      

FROM FACT_TABLE AS FAT
INNER JOIN GROUPS AS FTS ON FAT.DIM_PROJECT_ID = FTS.DIM_PROJECT_ID
GROUP BY FAT.DIM_BUILDING_ID, FAT.BUILDING_NAME;

【参考方案1】：

我会这样做：

select bn.building_name ,
       t.*
from ( select fat.building_id ,
              sum( case when fat.percentage_used <= 0.10                                then 1 else 0 end ) as group_a ,
              sum( case when fat.percentage_used >  0.10 and fat.percentage_used < 0.50 then 1 else 0 end ) as group_b ,
              sum( case when fat.percentage_used >= 0.50 and fat.percentage_used < 1.00 then 1 else 0 end ) as group_c ,
              sum( case when fat.percentage_used >= 1.00                                then 1 else 0 end ) as group_d ,
              sum( case when fat.percentage_used is null                                then 1 else 0 end ) as group_e
       from fact_table fat
       join groups     fts on tfs.dim_project_id = fat.dim_project_id
       group by fat.building_id
     ) t
join fact_table bn on bn.building_id = t.building_id

【讨论】：

添加范围的想法不错，但根据问题中的值，没有迹象表明需要范围。

【参考方案2】：

不要将聚合作为THEN，而是将CASE 语句包装在聚合中：

SELECT
SUM(CAST(FTS.GROUP_A AS BIGINT)) AS GROUP_A,
        SUM(CAST(FTS.GROUP_B AS BIGINT)) AS GROUP_B,
        SUM(CAST(FTS.GROUP_C AS BIGINT)) AS GROUP_C,  
        SUM(CASE WHEN FAT.PERCENTAGE_USED <= '0.10' THEN 1 ELSE 0 END) AS PROJECTS_L10,
        SUM(CASE WHEN FAT.PERCENTAGE_USED >= '0.50' THEN 1 ELSE 0 END) AS PROJECTS_G50,
        SUM(CASE WHEN FAT.PERCENTAGE_USED >= '1.00' THEN 1 ELSE 0 END) AS PROJECTS_G100,
        DAYS(DATE('2014-07-01')) - DAYS(CURRENT DATE)  AS DAYS_LEFT,
        (DAYS(DATE('2014-07-01')) - DAYS(CURRENT DATE))/7 AS WEEKS_LEFT, 
        DAYS(DATE('2013-12-31')) - DAYS(CURRENT DATE) AS DAYS_LEFT_YEAR      

FROM FACT_TABLE AS FAT
INNER JOIN GROUPS AS FTS ON FAT.DIM_PROJECT_ID = FTS.DIM_PROJECT_ID
GROUP BY FAT.DIM_BUILDING_ID, FAT.BUILDING_NAME;

ELSE 0 不是必需的，但有些人喜欢在查询中看到它。

或者，这也应该有效：

COUNT(CASE WHEN FAT.PERCENTAGE_USED >= '0.50' THEN 1 END) AS PROJECTS_G50,

【讨论】：

实际上，您选择了最后一个，但很乐意提供帮助。