Question

我试图仅根据两列中子字符串的标准显示最新记录。

SELECT convert(varchar, DateTime, 100) AS "Date and Time"
    ,Text2 AS Area
    ,Substring(Text1, 1,Charindex('/', Text1)-1) AS Device
    ,(Substring(Text1, Charindex('/', Text1)+1, LEN(Text1)) + Substring(PText6, Charindex(' ', PText6)+1, LEN(PText6))) AS Interlock
    ,Substring(PText7, 1,Charindex(':', PText7)-1) AS Username
FROM a_databse.dbo.a_view AS data
WHERE PText6 LIKE '%BypIn%' AND DateTime = (SELECT MAX(DateTime) FROM 
a_database.dbo.a_view WHERE Text1 = data.Text1 AND Interlock = data.Interlock AND PText6 LIKE 'Set%')

在最后一行

Interlock = data.Interlock

由于列名“ Interlock”无效，因此需要替换以进行正确的分组。但是，它将仅接受真实的列引用，例如：

Text1 = data.Text1

但使用子字符串：

Substring(PText6, Charindex(' ', PText6)+1, LEN(PText6)) = data.Substring(PText6, Charindex(' ', PText6)+1, LEN(PText6))

会抛出错误：

Cannot find either column "data" or the user-defined function or aggregate "data.Substring", or the name is ambiguous

Answer 1

您需要正确复制粘贴所有表达式，例如data.SUBSTRING(PText6, ...)应该是SUBSTRING(data.PText6, ...)。但是您可以使用CROSS APPLY来简化查询：

SELECT CONVERT(varchar, DateTime, 100) AS "Date and Time"
     , Text2 AS Area
     , data_vars.Device
     , data_vars.Interlock
     , data_vars.Username
FROM a_databse.dbo.a_view AS data
CROSS APPLY (
    SELECT SUBSTRING(Text1, 1, CHARINDEX('/', Text1) - 1) AS Device
         , SUBSTRING(Text1, CHARINDEX('/', Text1) + 1, LEN(Text1)) + SUBSTRING(PText6, CHARINDEX(' ', PText6) + 1, LEN(PText6)) AS Interlock
         , SUBSTRING(PText7, 1, CHARINDEX(':', PText7) - 1) AS Username
) AS data_vars
-- all columns inside data_vars are now accessible inside WHERE, GROUP BY, SELECT and ORDER BY
WHERE PText6 LIKE '%BypIn%' AND DateTime = (
    SELECT MAX(DateTime)
    FROM a_database.dbo.a_view
    WHERE Text1 = data.Text1 AND Interlock = data_vars.Interlock AND PText6 LIKE 'Set%'
)

仅显示按两列的子字符串分组的最新记录

1 个答案: