Thank you again @clintandrewhall for your help.
As I told you before : I have multiple charts in my dashboard and I am querying data from different indexes. Let's say I have two pie charts : the 1st is displaying SUM(costs) and different resources (for this I am relying on "index1"). And the 2nd chart is displaying COUNT(status) and different status (for this I am depending on "index2").
For the filter I am using these SQL commands :
SELECT category
FROM index1
WHERE category!='null'
GROUP BY category
->I've chosen "category" for "values column" also for "filter column"
For the record, "category" is shared by both indexes by that I mean that "category" is a common field for both indexes.
So basically the filter will be applied only on the 1st pie chart however I need it to be applied on both charts. I found a solution which is to use two filters and assign each one for each chart based on "filter group name". However, I want to use just one dropdown column.
I hope that my situation is clear now