SQL "IN" CLAUSE Performance issue

Question

I have a simple SQL statement:

select * from Employee 
where LEFT(REPLACE(EmployeeName,'.',''),4) IN ('ABCE', 'BCDS', 'EDSC', 'XDSD', 'EFSE')

And I am trying to do this in Linq:

Employees.Where(x => new[] { "ABCE", "BCDS", "EDSC", "XDSD", "EFSE" }.Contains((x.EmployeeName.Replace(".", "").Substring(0, 4))));

but the SQL statement it generates is not efficient. The EmployeeName is updated everytime before comparing to the strings instead of just once:

SELECT 
[Extent1].[EmployeeID] AS [EmployeeID], 
[Extent1].[EmployeeName] AS [EmployeeName], 
[Extent1].[EmployeeTypeID] AS [EmployeeTypeID], 
[Extent1].[Active] AS [Active]
FROM [dbo].[Employee] AS [Extent1]
WHERE (N'ABCE' = (SUBSTRING(REPLACE([Extent1].[EmployeeName], N'.', N''), 0 + 1, 4))) 
OR (N'BCDS' = (SUBSTRING(REPLACE([Extent1].[EmployeeName], N'.', N''), 0 + 1, 4))) 
OR (N'EDsC' = (SUBSTRING(REPLACE([Extent1].[EmployeeName], N'.', N''), 0 + 1, 4))) 
OR (N'XDSs' = (SUBSTRING(REPLACE([Extent1].[EmployeeName], N'.', N''), 0 + 1, 4))) 
OR (N'EFSE' = (SUBSTRING(REPLACE([Extent1].[EmployeeName], N'.', N''), 0 + 1, 4)))

How can I make the generated SQL look more like the original sql statement? Thanks

Answer 1

I only tested it with linqpad but i think this will generate a more efficient query.

var result = from record in Employee
             let name = record.EmployeeName.Replace( ".", "" ).Substring( 0, 4 )
             where new[] { "ABCE", "BCDS", [...] }.Contains( name )
             select record;

Answer 2

This is strange, but I rewrote your query and generated sql statement was

WHERE (SUBSTRING(REPLACE([Extent1].[EmployeeName], N'.', N''), 0 + 1, 4) IN (N'ABCE', N'BCDS', N'EDSC', N'XDSD', N'EFSE')) AND (SUBSTRING(REPLACE([Extent1].[Name], N'.', N'')

I guess that depends on used database and framework (in my case SQL Server 2008 and EF).

If you are using EF, you can force EF to use your sql statement

context.Set<Employee>().SqlQuery("select * from Employee where LEFT(REPLACE(EmployeeName,'.',''),4) IN ('ABCE', 'BCDS', 'EDSC', 'XDSD', 'EFSE')");