SQL Server - Where 条件使用答案

【问题标题】：SQL Server - Where condition usageSQL Server - Where 条件使用
【发布时间】：2015-09-21 09:07:16
【问题描述】：

我想在下面的选择 sql 代码中添加条件。

select rtrim(ltrim(SUBSTRING(line,1,CHARINDEX('|',line) -1))) as drivename
      ,round(cast(rtrim(ltrim(SUBSTRING(line,CHARINDEX('|',line)+1,
      (CHARINDEX('%',line) -1)-CHARINDEX('|',line)) )) as Float)/1024,0) as 'capacity(GB)'
      ,round(cast(rtrim(ltrim(SUBSTRING(line,CHARINDEX('%',line)+1,
      (CHARINDEX('*',line) -1)-CHARINDEX('%',line)) )) as Float) /1024 ,0)as 'freespace(GB)'
from #output
where line like '[A-Z][:]%'
order by drivename

结果是;

drivename   capacity(GB)    freespace(GB) 
C:\            120                36 
D:\            100                 7

我想这样添加：'freespace(GB) > 10'

如何添加这个条件？

【问题讨论】：

标签： sql sql-server tsql

【解决方案1】：

使用 CTE 或子查询：

;WITH cte as
(
select rtrim(ltrim(SUBSTRING(line,1,CHARINDEX('|',line) -1))) as drivename
      ,round(cast(rtrim(ltrim(SUBSTRING(line,CHARINDEX('|',line)+1,
      (CHARINDEX('%',line) -1)-CHARINDEX('|',line)) )) as Float)/1024,0) as 'capacity(GB)'
      ,round(cast(rtrim(ltrim(SUBSTRING(line,CHARINDEX('%',line)+1,
      (CHARINDEX('*',line) -1)-CHARINDEX('%',line)) )) as Float) /1024 ,0)as 'freespace(GB)'
from #output
where line like '[A-Z][:]%'
)
SELECT *
FROM cte
WHERE [freespace(GB)] > 10
order by drivename;

第二个是不理解的经典例子Logical Query Processing

【讨论】：

【解决方案2】：

select rtrim(ltrim(SUBSTRING(line,1,CHARINDEX('|',line) -1))) as drivename
      ,round(cast(rtrim(ltrim(SUBSTRING(line,CHARINDEX('|',line)+1,
      (CHARINDEX('%',line) -1)-CHARINDEX('|',line)) )) as Float)/1024,0) as 'capacity(GB)'
      ,round(cast(rtrim(ltrim(SUBSTRING(line,CHARINDEX('%',line)+1,
      (CHARINDEX('*',line) -1)-CHARINDEX('%',line)) )) as Float) /1024 ,0)as 'freespace(GB)'
from #output
where line like '[A-Z][:]%'
AND round(cast(rtrim(ltrim(SUBSTRING(line,CHARINDEX('%',line)+1,
      (CHARINDEX('*',line) -1)-CHARINDEX('%',line)) )) as Float) /1024 ,0) > 10
order by drivename

如果您只想显示上述查询的 C:\ 信息。

【讨论】：

@sezercan 尝试使用AND round(cast(rtrim(ltrim(SUBSTRING(line,CHARINDEX('%',line)+1, (CHARINDEX('*',line) -1)-CHARINDEX('%',line)) )) as Float) /1024 ,0) > 10，但你的代码会重复且丑陋
@Abhishek 你只使用了部分表达式，计算freesize有2行

【解决方案3】：

有多种方法可以做到这一点。Temp table 和 CTE 可能看起来相同，但请尝试从 here. 了解它们之间的区别

使用临时表

select * into ##t from 
    (select rtrim(ltrim(SUBSTRING(line,1,CHARINDEX('|',line) -1))) as drivename,
    round(cast(rtrim(ltrim(SUBSTRING(line,CHARINDEX('|',line)+1,
    (CHARINDEX('%',line) -1)-CHARINDEX('|',line)) )) as Float)/1024,0) as 'capacity(GB)',
    round(cast(rtrim(ltrim(SUBSTRING(line,CHARINDEX('%',line)+1,
    (CHARINDEX('*',line) -1)-CHARINDEX('%',line)) )) as Float) /1024 ,0)as 'freespace(GB)'
    from #output
    where line like '[A-Z][:]%') as T

Select * from ##t where [freespace(GB)] > 10 order by drivename

通过使用 CTE

;WITH cte as
(
select rtrim(ltrim(SUBSTRING(line,1,CHARINDEX('|',line) -1))) as drivename
      ,round(cast(rtrim(ltrim(SUBSTRING(line,CHARINDEX('|',line)+1,
      (CHARINDEX('%',line) -1)-CHARINDEX('|',line)) )) as Float)/1024,0) as 'capacity(GB)'
      ,round(cast(rtrim(ltrim(SUBSTRING(line,CHARINDEX('%',line)+1,
      (CHARINDEX('*',line) -1)-CHARINDEX('%',line)) )) as Float) /1024 ,0)as 'freespace(GB)'
from #output
where line like '[A-Z][:]%'
)

SELECT * FROM cte WHERE [freespace(GB)] > 10 order by drivename;

直接在where子句中使用条件

select rtrim(ltrim(SUBSTRING(line,1,CHARINDEX('|',line) -1))) as drivename,
round(cast(rtrim(ltrim(SUBSTRING(line,CHARINDEX('|',line)+1,
(CHARINDEX('%',line) -1)-CHARINDEX('|',line)) )) as Float)/1024,0) as 'capacity(GB)',
round(cast(rtrim(ltrim(SUBSTRING(line,CHARINDEX('%',line)+1,
(CHARINDEX('*',line) -1)-CHARINDEX('%',line)) )) as Float) /1024 ,0)as 'freespace(GB)'
from #output
where line like '[A-Z][:]%'
And (round(cast(rtrim(ltrim(SUBSTRING(line,CHARINDEX('%',line)+1,
(CHARINDEX('*',line) -1)-CHARINDEX('%',line)) )) as Float) /1024 ,0)) > 10
order by drivename

【讨论】：