Question

下面必须有更好的方法来编写查询，如果您有任何建议，请告诉我。

SELECT *
FROM 
    [eSDR_Full].[dbo].[course_register]
WHERE
    broad_field_code = '08'  
    AND narrow_field_code = '05' 
    AND detail_field_code = '05' 
    AND end_month is null 
    AND disabled <> 'Y'

    OR broad_field_code = '08' 
    AND narrow_field_code = '05' 
    AND detail_field_code = '05'
    AND end_month > '201512' 
    AND disabled <> 'Y'

    OR broad_field_code = '08' 
    AND narrow_field_code = '05' 
    AND detail_field_code = '05' 
    AND end_month is null 
    AND disabled is null

    OR broad_field_code = '08' 
    AND narrow_field_code = '05' 
    AND detail_field_code = '05'
    AND end_month > '201512' 
    AND disabled is null

ORDER BY
    end_month DESC

Answer 1

首次重构：

SELECT *
  FROM [eSDR_Full].[dbo].[course_register]
  Where (broad_field_code = '08' and narrow_field_code = '05' and detail_field_code = '05')
     and (   (end_month is null and disabled <> 'Y')
          or (end_month > '201512' and disabled <> 'Y')
          or (end_month is null and disabled is null)
          or (end_month > '201512' and disabled is null))
 order by end_month desc

这清楚地表明您对所有条件都有一个共同的前缀。

第二次重构利用了其他共性：

SELECT *
  FROM [eSDR_Full].[dbo].[course_register]
  Where (broad_field_code = '08' and narrow_field_code = '05' and detail_field_code = '05')
     and (end_month is null or end_month > '201512')
     and (disabled is null or disabled <> 'Y')
 order by end_month desc

现在很明显，我们只是根据每个列的简单条件有一系列堆叠的AND，所以我们可以这样做：

SELECT *
  FROM [eSDR_Full].[dbo].[course_register]
  Where broad_field_code = '08' 
    and narrow_field_code = '05' 
    and detail_field_code = '05'
    and coalesce(end_month, '999999') > '201512'
    and coalesce(disabled, 'N') <> 'Y')
 order by end_month desc

Answer 2

这应该有效：

SELECT *
FROM [eSDR_Full].[dbo].[course_register]
WHERE broad_field_code = '08' 
    AND narrow_field_code = '05' 
    AND detail_field_code = '05' 
    AND (end_month IS NULL OR end_month > '201512')
    AND ISNULL(disabled,'') != 'Y'
ORDER BY end_month DESC

SQL - 如何合并或语句

2 个答案: