#434

backend/app/services/counts_axes.rb

@@ -61,7 +61,11 @@ class CountsAxes
             expression, axis.fetch('grain', 'month'), @population.timezone) : expression
       end
       if !HistoryAccess.admin? && !PUBLIC_FIELDS.include?(field)
-        expression = "CASE WHEN #{ HistoryAccess.sql(@definition.model, 'v') } " +
+        visible = HistoryAccess.sql(@definition.model, 'v')
+        if field == 'changed_field'
+          visible = "(#{ visible }) AND (#{ HistoryAccess.sql(@definition.model, 'previous') })"
+        end
+        expression = "CASE WHEN #{ visible } " +
             "THEN CAST((#{ expression }) AS CHAR) ELSE '#{ MASKED_VALUE }' END"
       end
       expression
@@ -72,8 +76,10 @@ class CountsAxes
     return 'COUNT(DISTINCT v.id)' unless rows.any? { _1['field'] == 'tags' }
 
     # Keep tag occurrences even when several private tags share one masked label.
-    "COUNT(DISTINCT v.id, COALESCE(CONCAT('internal:', tag_entry.tag_id), " +
-        "CONCAT('external:', tag_entry.external_tag_id)))"
+    values = ['v.id', "COALESCE(CONCAT('internal:', tag_entry.tag_id), " +
+        "CONCAT('external:', tag_entry.external_tag_id))"]
+    values << 'changed.field_key' if rows.any? { _1['field'] == 'changed_field' }
+    "COUNT(DISTINCT #{ values.join(', ') })"
   end
 
   def joins(fields = all.map { _1['field'] })