Cannot connect variables with table query


I am new to Grafana and trying and testing it for the first time. I have a simple table with a set of columns. I want to be able to select a particular column or contents of a particular column from the dashboard variables (drop-down-list). I believe that entering anything in the variables panel gets inserted in a query.

I want to know the pattern or the actual query by which I can select a particular value from the drop-down list.

My query in the drop-down list is:
Select “Root_Cause” from alarm

My table, in the datatabase looks like this
Element | Element_Type | Status | Root_Cause | Classification

My Table panel query looks like this:
SELECT * from alarm where ‘Root_Cause’ = ‘$Value’

Where am I going wrong? How can I select values from the drop-down list that might be inserted into the values tab?

What Grafana version are you using? v5.4.2

What data source are you using? PostgreSQL

What OS are you running grafana on? Windows

Thank you in advance.Variables