@Hossein: I am also facing issue while trying to add url inside existing chart. In my case I have to first make chart(pivot table using integer value as matrics) and then i have to add link with those value .
If I go through explore view by adding url in begining then it converts the column from integer to string and with string we can not make metrics required to make pivot chart.
So if any solution to add link in existing chart value it would be greatful.
currently it just reflecting
<a href="/superset/dashboard/86/" target="_blank">442</a> as column value.