Using Case to match strings in sql server?

Question

I am trying to use CASE in a SQL Select statement that will allow me to get results where I can utilize the length of one string to produce the resutls of another string. These are for non-matched records from two data sets that share a common ID, but variant Data Source.

Case statement is below:

Select Column1, Column2, 
Case
When Column1 = 'Something" and Len(Column2) = '35' Then Column1 = "Something Else" and substring(Column2, 1, 35)
End as Column3
From  dbo.xxx

When I run it I get the following error:

Msg 102, Level 15, State 1, Line 5 Incorrect syntax near '='.

Answer 1

You need to have a value for each WHEN, and ought to have an ELSE:

Select Data_Source, CustomerID,
  CASE
    WHEN Data_Source = 'Test1' and Len(CustomerName) = 35 THEN 'First Value'
    WHEN Data_Source = 'Test2' THEN substring(CustomerName, 1, 35)
    ELSE 'Sorry, no match.'
    END AS CustomerName
  From dbo.xx

FYI: Len() doesn't return a string.

EDIT: A SQL Server answer that addresses some of the comments might be:

declare @DataSource as Table ( Id Int Identity, CustomerName VarChar(64) )
declare @VariantDataSource as Table ( Id Int Identity, CostumerName VarChar(64) )
insert into @DataSource ( CustomerName ) values ( 'Alice B.' ), ( 'Bob C.' ), ( 'Charles D.' )
insert into @VariantDataSource ( CostumerName ) values ( 'Blush' ), ( 'Dye' ), ( 'Pancake Base' )

select *,
  -- Output the CostumerName padded or trimmed to the same length as CustomerName.  NULLs are not handled gracefully.
  Substring( CostumerName + Replicate( '.', Len( CustomerName ) ), 1, Len( CustomerName ) ) as Clustermere,
  -- Output the CostumerName padded or trimmed to the same length as CustomerName.  NULLs in CustomerName are explicitly handled.
  case
    when CustomerName is NULL then ''
    when Len( CustomerName ) > Len( CostumerName ) then Substring( CostumerName, 1, Len( CustomerName ) )
    else Substring( CostumerName + Replicate( '.', Len( CustomerName ) ), 1, Len( CustomerName ) )
    end as 'Crustymore'
  from @DataSource as DS inner join
    @VariantDataSource as VDS on VDS.Id = DS.Id

Answer 2

Select 
    Column1, 
    Column2, 
    Case 
      When Column1 = 'Something' and Len(Column2) = 35 
      Then 'Something Else' + substring(Column2, 1, 35) 
    End as Column3 
From dbo.xxx

Update your query on

1. use '+' for string concat
2. len() returns int, no need to use ''
3. remove "Column1 =" in the case when condition
4. replace "" with ''

Hope this help.