Dynamic Column Selection In Stored Procedure

Hey Guys,

Here is the issue I'm having. I am writing a stored procedure that takes a couple of parameters. Each one is the value within a specific column in one table (i.e., @part = 'o-ring' or @sub_assembly = 'hydraulic ram'). Needless to say, the columns form a hierarchy. What I am trying to achieve is to allow the user to specify one of the parameters and get a count for all records where the specified value is in the corresponding column. So, if the user puts in the parameter @part = 'o-ring', I want it to know that the where clause for the select statement should look for o-ring in the part column and not the sub_assembly column. Here is what I am trying to do, which isn't working.

DECLARE @querycolumn varchar(20),
@queryvalue varchar(35)

SET @querycolumn = ''
SET @queryvalue = ''

IF(@sub_assembly = NULL)
BEGIN
IF(@part = NULL)
BEGIN
PRINT 'This is an error. You must have at least a part'
END
ELSE
BEGIN
SET @querycolumn = 'Part'
SET @queryvalue = @part
END
END
ELSE
BEGIN
SET @querycolumn = 'SubAssembly'
SET @queryvalue = @sub_assembly
END

SELECT SubAssembly, Part, COUNT(RecordID)
FROM Table
WHERE @querycolumn = @queryvalue
GROUP BY SubAssembly, Part
ORDER BY SubAssembly, Part

The problem is that I'm getting an error when I try to use @querycolumn to supply the column name to the WHERE clause. Any ideas or suggestions?