#434

backend/app/services/counts_pivot_totals.rb

@@ -8,6 +8,9 @@ class CountsPivotTotals
   end
 
   def call
+    # MySQL's unlimited LIMIT prevents CTE merging: authorise once for all branches.
+    basis = @population.scope.except(:select, :order).select('v.*')
+        .limit(18_446_744_073_709_551_615).to_sql
     queries = @rows.flat_map do |row_depth, headers|
       @columns.filter_map do |column_depth, columns|
         next if row_depth == @axes.rows.length && column_depth == @axes.columns.length
@@ -15,7 +18,7 @@ class CountsPivotTotals
         indexes = (0...row_depth).to_a +
             (0...column_depth).map { @axes.rows.length + _1 }
         expressions = indexes.map { @axes.expressions[_1] }
-        scope = @population.scope.except(:select, :order)
+        scope = @population.scope.except(:select, :order, :where, :from).from('authorised v')
         joins = @axes.joins(indexes.map { @axes.all[_1].fetch('field') })
         scope = scope.joins(joins) unless joins.empty?
         if row_depth.positive?
@@ -48,6 +51,7 @@ class CountsPivotTotals
 
     sql = queries.map { "(#{ _1 })" }.join(' UNION ALL ')
     @population.definition.model.connection.select_all(
+        "WITH authorised AS (#{ basis }) " +
         "SELECT /*+ MAX_EXECUTION_TIME(10000) */ * FROM (#{ sql }) totals").map do |record|
       row_depth = record['row_depth'].to_i
       column_depth = record['column_depth'].to_i