How to pass multiple Value to a dynamic Variable in Dashboard underlying SQL

Linglin
New Contributor III
select         {{user_defined_variable}} as my_var,
                   count(*) as cnt
from            my_table
where         {{user_defined_variable}} = {{value}}
 
for user_defined_variable, I use query based dropdown list to get a column_name I'd like in the selection. 
for user_defined_value, I can only use text to pass one value
 
Since the value selection is based on my selection of user_defined_variable, I can't use dropdown list to predefine value. I tried to nest variable in the query used for user_defined_variable. It doesn't work. 
I also tried {{user_defined_variable}} in ({{value}}), doesn't work as well. 
 
I wonder if anyone knows a solution. thanks!