variables in mysql

Ray, thank you in advance.
I have been trying for some time to understand how the testing block for mysql works. I have this simple q:

SELECT COUNT(pil_knotg_info.FID)
FROM pil_knotg_info
WHERE pil_knotg_info.FID = $FID_num LIMIT 1
====================
Now, when I enter FID_num as the variable name in the advanced test section, and then enter 226 (a record id to find) as the default value and also 226 as the run time value , I get the return message "unknown column '$226' in the WHERE clause". I cannot figure what else to enter here. Can you help, as my program which used to work now returns "You have a syntax error in your SQL statement" with no line numbers or any other help. I am trying to check each query one by one to find where the error might be.