Use variable sql for column name - sql

Question

Before you shout at me in CAPS for not searching - I have! Dynamic SQL is good, dynamic SQL is bad. Learning a lot..
I can accomplish what I'm after by using logic in there WHERE clause, but it adds a significant amount of run time. The query takes 8 seconds if I hard code the criteria and 1:20 if I use the WHERE logic.
Here is what I'd like to do:
Declare #EmployeeToggle varchar(30)
Declare #Employee_ID varchar(30)
Declare #EmployeeField varchar(100)
set #EmployeeToggle = '1'
set #Employee_ID = '1166'
set #EmployeeField = case when #EmployeeToggle = '1' then 'Field1' else
'Field2' end;
select * from Table1 where #EmployeeField = #Employee_ID
I don't think it's possible without dynamic sql. I still don't know whether or not I should use it. It's my thought that it would take the query back down to 8 seconds, because it would immediately know which field to use in the where clause.
Alternatively, a few ways to do it in the where only:
where (( not #EmployeeToggle = '1') or Field1 = #Employee_ID) and
(#EmployeeToggle = '1' or Field2 = #Employee_ID)
where (1=(case when #EmployeeToggle = '1' then 1 else 0 end ) or Field1 =
#Employee_ID)
and (1=(case when #EmployeeToggle = '2' then 1 else 0 end) or Field2 =
#Employee_ID)
These work great (admittedly I copied and pasted these examples), but at the expense of run time.
My final thought, and the way others have done it at my org, is to create two scripts that are identical except for the field used in the where clause. So, if #EmployeeToggle = '1' it will run the first script and if it's '2' it will run the second. I haven't tried that yet, but I assume the runtime will be closer to the 8 seconds at the expense of some ugly code.
Thanks for the help.

Answer 1

Why not just use a single query?
select t.*
from table1
where #EmployeeToggle = '1' and field_1 = #Employee_ID
union all
select t.*
from table1
where #EmployeeToggle <> '1' and field_2 = #Employee_ID;
By using union all, SQL Server should use indexes for each subquery -- and if you have indexes on the fields, the query should be fast.

Answer 2

You can stay with static SQL when using CASE expression in SELECT then filter it.
SELECT *
FROM (
SELECT *,
CASE WHEN #EmployeeToggle = '1' THEN Field1 ELSE Field2 END AS Field1_2
FROM Table1
) t
WHERE
Field1_2 = #Employee_ID

Answer 3

Here is your dynamic query:
Declare #EmployeeToggle varchar(30)
Declare #Employee_ID varchar(30)
Declare #EmployeeField varchar(100)
set #EmployeeToggle = '1'
set #Employee_ID = '1166'
set #EmployeeField = case when #EmployeeToggle = '1' then 'Field1' else
'Field2' end;
DECLARE #SQLString VARCHAR(MAX)
SET #SQLString='select *
from Table1
where '+#EmployeeField+' = '+#Employee_ID+''
PRINT(#SQLString) --If you want to check actual query
EXEC(#SQLString)