将varchar值转换为int数据类型时，SQL Select Case Conversion失败。

Question

Folks, I've read the fixes for this issue but I have a variation that I can't solve.

Firstly the following syntax throws the error

 Case
    when #TFs.lTFID = 1161165 then REPLACE(CONVERT(VARCHAR(11), cast([dCreatedUTC] as datetime), 106), ' ', '-')
    when #TFs.lTFID = 1161166 then 'Administrator'
    when #TFs.lTFID = 1161167 then ''
    when #TFs.lTFID = 1161168 then AssetID
    when #TFs.lTFID = 1161169 then ''
    when #TFs.lTFID = 1161170 then ''
    when #TFs.lTFID = 1161172 then ''
    when #TFs.lTFID = 1161173 then ''
    else CAST(#TFs.lTFID as varchar(20))
  End 'Value'

If I comment out all but one of the "when" lines as below it works.

 Case
    when #TFs.lTFID = 1161165 then REPLACE(CONVERT(VARCHAR(11), cast([dCreatedUTC] as datetime), 106), ' ', '-')
/*  when #TFs.lTFID = 1161166 then 'Administrator'
    when #TFs.lTFID = 1161167 then ''
    when #TFs.lTFID = 1161168 then AssetID
    when #TFs.lTFID = 1161169 then ''
    when #TFs.lTFID = 1161170 then ''
    when #TFs.lTFID = 1161172 then ''
    when #TFs.lTFID = 1161173 then ''*/
    else CAST(#TFs.lTFID as varchar(20))
  End 'Value'

Any thoughts about how I can format this query so that all "cases" work?

Answer 1

Based on the error message, the result of the CASE expressions gets converted to INT . Also of the return value of your WHEN s is known to be VARCHAR , except for AssetID , so I assume this must be an INT value.

The error happens because when using a CASE expression, all return values must be of the same data type. In case they have different data types, all values are converted to the type with a higher data type precedence .

And since INT has a higher precedence than VARCHAR , the results are converted to INT which caused the error. To fix this, you have to convert AssetID to VARCHAR(n) also

Case
    when #TFs.lTFID = 1161165 then REPLACE(CONVERT(VARCHAR(11), cast([dCreatedUTC] as datetime), 106), ' ', '-')
    when #TFs.lTFID = 1161166 then 'Administrator'
    when #TFs.lTFID = 1161167 then ''
    when #TFs.lTFID = 1161168 then CAST(AssetID AS VARCHAR(20))
    when #TFs.lTFID = 1161169 then ''
    when #TFs.lTFID = 1161170 then ''
    when #TFs.lTFID = 1161172 then ''
    when #TFs.lTFID = 1161173 then ''
    else CAST(#TFs.lTFID as varchar(20))
End 'Value'

Answer 2

Try and cast the AssetID to a varchar in the case statement.

Case
    when #TFs.lTFID = 1161165 then REPLACE(CONVERT(VARCHAR(11), cast([dCreatedUTC] as datetime), 106), ' ', '-')
    when #TFs.lTFID = 1161166 then 'Administrator'
    when #TFs.lTFID = 1161167 then ''
    when #TFs.lTFID = 1161168 then CAST(AssetID AS VARCHAR(20))
    when #TFs.lTFID = 1161169 then ''
    when #TFs.lTFID = 1161170 then ''
    when #TFs.lTFID = 1161172 then ''
    when #TFs.lTFID = 1161173 then ''
    else CAST(#TFs.lTFID as varchar(20))
  End 'Value'

Answer 3

Try this

Case #TFs.lTFID
 When 1161165 then REPLACE(CONVERT(VARCHAR(11), cast([dCreatedUTC] as datetime), 106), ' ', '-')
 When 1161166 then 'Administrator'
 .
 .
 .
 Else CAST(#TFs.lTFID as varchar(20)) END

Answer 4

Put your CAST outside the the CASE as follows:

     CAST(
             Case
                when #TFs.lTFID = 1161165 then REPLACE(CONVERT(VARCHAR(11), cast([dCreatedUTC] as datetime), 106), ' ', '-')
                when #TFs.lTFID = 1161166 then 'Administrator'
                when #TFs.lTFID = 1161167 then ''
                when #TFs.lTFID = 1161168 then AssetID
                when #TFs.lTFID = 1161169 then ''
                when #TFs.lTFID = 1161170 then ''
                when #TFs.lTFID = 1161172 then ''
                when #TFs.lTFID = 1161173 then ''
                else #TFs.lTFID
              End 
         as varchar(20)) 'Value'