如何计算来自多列的空值

问题描述

| 我的SQL 2005表中有以下数据模式：

MPAN,Date,Reading1,Reading2,Reading3,......,Reading48

134,21/05/11,0.345,0.789

134,22/05/11,0.467

456,1.234

456,0.009,0.534,......

223,........,3.345

223,3.223,1.234,....,0.989

对于每个记录行，具有丢失数据的字段的数量不同。我如何找出每行缺少多少文件的字段（按MPAN和日期分组）。曾经在Google上进行过搜索，似乎有人建议针对类似情况下的存储过程？ 请你帮忙     

解决方法

select MPAN,Date,sum
          (
            case when Reading1 is null then 1 else 0 end +
            case when Reading2 is null then 1 else 0 end +
            case when Reading3 is null then 1 else 0 end
          ) as NullCount
from T
group by MPAN,Date

    ,通常的方法是使用

CASE

：

SELECT CASE WHEN field_1 IS NULL THEN 1 ELSE 0 END
       + CASE WHEN field_2 IS NULL THEN 1 ELSE 0 END
       + ... AS total_nulls,COUNT(*) as num_rows
FROM table 
GROUP BY total_nulls;

使用问题中的分组和字段名称：

SELECT MPAN,SUM(CASE WHEN Reading1 IS NULL THEN 1 ELSE 0 END
       + CASE WHEN Reading2 IS NULL THEN 1 ELSE 0 END
       + ... ) AS total_nulls
FROM table 
GROUP BY MPAN,Date;

    ,

SELECT
  MPAN,NullCount = COUNT(*) * 48
    - COUNT(Reading1)
    - COUNT(Reading2)
    - COUNT(Reading3)
    …
    - COUNT(Reading48)
FROM atable
GROUP BY MPAN,Date

    ,使用case语句计算总和：

select MPAN,date,sum(null_cnt) from (
  select MPAN,(case when val1 is null then 1 else 0 end) +
  (case when val2 is null then 1 else 0 end) + ...
  (case when val48 is null then 1 else 0 end) null_cnt
  from ...
) group by MPAN,date

    ,恐怕你不得不做些丑陋的事情

select MPAN,(
    CASE WHEN Reading1 is null then 1 else 0 end +
    CASE WHEN Reading2 is null then 1 else 0 end +
    CASE WHEN Reading3 is null then 1 else 0 end +
    CASE WHEN Reading4 is null then 1 else 0 end +
    ... +
    CASE WHEN Reading48 is null then 1 else 0 end
) as CountOfNulls

from YourTable

    ,如果您可以更改架构，那么我要做的第一件事就是将其分解为三个表： \'Readings \'，带有ID和名称，值类似于

ID  Name
1   Reading1
2   Reading2
...
48  Reading48

这无疑使您可以轻松添加更多内容。 接下来，一个\'MPAN \'表，其中包含\'MPAN \'s，ID，MPAN和日期：

ID MPAN Date
1  134  21/05/11
2  134  22/05/11

最后，是一个\'Score \'表，该表将两者相关联，并包含具有ReadingID，MPANID和Score的分数：

MPANID ReadingID Score
1      3         0.345
1      48        0.789
2      48        0.467

然后，您可以让关系数据库执行其最擅长的工作并利用关系。例如，此查询将获取所有具有Reading2得分的MPAN：

SELECT MPAN.*,Scores.Score
  FROM MPAN
  JOIN Scores ON Scores.MPANID = MPAN.ID
             AND Scores.ReadingID = 2

    ,用这个

select 
MPAN,coalesce(isnull(reading1,0)+isnull(reading2,0)+isnull(reading3,0)+isnull(reading4,0),0) 
from 
tablename