3 files changed, 18 insertions, 8 deletions
diff --git a/activerecord/lib/active_record/relation/batches.rb b/activerecord/lib/active_record/relation/batches.rb
index 2fd89882ff..14701f668c 100644
--- a/activerecord/lib/active_record/relation/batches.rb
+++ b/activerecord/lib/active_record/relation/batches.rb
@@ -59,11 +59,11 @@ module ActiveRecord
         relation = apply_finder_options(finder_options)
       end
 
-      start = options.delete(:start).to_i
+      start = options.delete(:start)
       batch_size = options.delete(:batch_size) || 1000
 
       relation = relation.reorder(batch_order).limit(batch_size)
-      records = relation.where(table[primary_key].gteq(start)).all
+      records = start ? relation.where(table[primary_key].gteq(start)).to_a : relation.to_a
 
       while records.any?
         records_size = records.size
diff --git a/activerecord/lib/active_record/relation/calculations.rb b/activerecord/lib/active_record/relation/calculations.rb
index 802059db21..1f9dbdc3d4 100644
--- a/activerecord/lib/active_record/relation/calculations.rb
+++ b/activerecord/lib/active_record/relation/calculations.rb
@@ -177,8 +177,15 @@ module ActiveRecord
     #   Person.where(:confirmed => true).limit(5).pluck(:id)
     #
     def pluck(column_name)
-      column_name = column_name.to_s
-      klass.connection.select_all(select(column_name).arel).map! do |attributes|
+      if column_name.is_a?(Symbol) && column_names.include?(column_name.to_s)
+        column_name = "#{connection.quote_table_name(table_name)}.#{connection.quote_column_name(column_name)}"
+      else
+        column_name = column_name.to_s
+      end
+
+      relation = clone
+      relation.select_values = [column_name]
+      klass.connection.select_all(relation.arel).map! do |attributes|
         klass.type_cast_attribute(attributes.keys.first, klass.initialize_attributes(attributes))
       end
     end
@@ -188,7 +195,8 @@ module ActiveRecord
     def perform_calculation(operation, column_name, options = {})
       operation = operation.to_s.downcase
 
-      distinct = options[:distinct]
+      # If #count is used in conjuction with #uniq it is considered distinct. (eg. relation.uniq.count)
+      distinct = options[:distinct] || self.uniq_value
 
       if operation == "count"
         column_name ||= (select_for_count || :all)
diff --git a/activerecord/lib/active_record/relation/finder_methods.rb b/activerecord/lib/active_record/relation/finder_methods.rb
index abc67d9c15..08cfe4f70d 100644
--- a/activerecord/lib/active_record/relation/finder_methods.rb
+++ b/activerecord/lib/active_record/relation/finder_methods.rb
@@ -253,9 +253,11 @@ module ActiveRecord
       orders = relation.order_values.map { |val| val.presence }.compact
       values = @klass.connection.distinct("#{@klass.connection.quote_table_name table_name}.#{primary_key}", orders)
 
-      relation = relation.dup
+      relation = relation.dup.select(values)
+
+      id_rows = @klass.connection.select_all(relation.arel, 'SQL', relation.bind_values)
+      ids_array = id_rows.map {|row| row[primary_key]}
 
-      ids_array = relation.select(values).collect {|row| row[primary_key]}
       ids_array.empty? ? raise(ThrowResult) : table[primary_key].in(ids_array)
     end
 
@@ -263,7 +265,7 @@ module ActiveRecord
       conditions = Hash[attributes.map {|a| [a, args[attributes.index(a)]]}]
       result = where(conditions).send(match.finder)
 
-      if match.bang? && result.blank?
+      if match.bang? && result.nil?
         raise RecordNotFound, "Couldn't find #{@klass.name} with #{conditions.to_a.collect {|p| p.join(' = ')}.join(', ')}"
       else
         yield(result) if block_given?