Handle UPDATE/DELETE with OFFSET in Arel

activerecord/lib/active_record/relation.rb

@@ -356,11 +356,12 @@ module ActiveRecord
         stmt.set Arel.sql(klass.sanitize_sql_for_assignment(updates, table.name))
       end
 
-      if has_join_values? || offset_value
+      if has_join_values?
         @klass.connection.join_to_update(stmt, arel, arel_attribute(primary_key))
       else
         stmt.key = arel_attribute(primary_key)
         stmt.take(arel.limit)
+        stmt.offset(arel.offset)
         stmt.order(*arel.orders)
         stmt.wheres = arel.constraints
       end
@@ -484,11 +485,12 @@ module ActiveRecord
       stmt = Arel::DeleteManager.new
       stmt.from(table)
 
-      if has_join_values? || offset_value
+      if has_join_values?
         @klass.connection.join_to_delete(stmt, arel, arel_attribute(primary_key))
       else
         stmt.key = arel_attribute(primary_key)
         stmt.take(arel.limit)
+        stmt.offset(arel.offset)
         stmt.order(*arel.orders)
         stmt.wheres = arel.constraints
       end

activerecord/lib/arel/nodes/delete_statement.rb

@@ -3,7 +3,7 @@
 module Arel # :nodoc: all
   module Nodes
     class DeleteStatement < Arel::Nodes::Node
-      attr_accessor :left, :right, :orders, :limit, :key
+      attr_accessor :left, :right, :orders, :limit, :offset, :key
 
       alias :relation :left
       alias :relation= :left=
@@ -16,6 +16,7 @@ module Arel # :nodoc: all
         @right = wheres
         @orders = []
         @limit = nil
+        @offset = nil
         @key = nil
       end
 
@@ -26,7 +27,7 @@ module Arel # :nodoc: all
       end
 
       def hash
-        [self.class, @left, @right, @orders, @limit, @key].hash
+        [self.class, @left, @right, @orders, @limit, @offset, @key].hash
       end
 
       def eql?(other)
@@ -35,6 +36,7 @@ module Arel # :nodoc: all
           self.right == other.right &&
           self.orders == other.orders &&
           self.limit == other.limit &&
+          self.offset == other.offset &&
           self.key == other.key
       end
       alias :== :eql?

activerecord/lib/arel/nodes/update_statement.rb

@@ -3,7 +3,7 @@
 module Arel # :nodoc: all
   module Nodes
     class UpdateStatement < Arel::Nodes::Node
-      attr_accessor :relation, :wheres, :values, :orders, :limit, :key
+      attr_accessor :relation, :wheres, :values, :orders, :limit, :offset, :key
 
       def initialize
         @relation = nil
@@ -11,6 +11,7 @@ module Arel # :nodoc: all
         @values   = []
         @orders   = []
         @limit    = nil
+        @offset   = nil
         @key      = nil
       end
 
@@ -21,7 +22,7 @@ module Arel # :nodoc: all
       end
 
       def hash
-        [@relation, @wheres, @values, @orders, @limit, @key].hash
+        [@relation, @wheres, @values, @orders, @limit, @offset, @key].hash
       end
 
       def eql?(other)
@@ -31,6 +32,7 @@ module Arel # :nodoc: all
           self.values == other.values &&
           self.orders == other.orders &&
           self.limit == other.limit &&
+          self.offset == other.offset &&
           self.key == other.key
       end
       alias :== :eql?

activerecord/lib/arel/tree_manager.rb

@@ -10,6 +10,11 @@ module Arel # :nodoc: all
         self
       end
 
+      def offset(offset)
+        @ast.offset = Nodes::Offset.new(Nodes.build_quoted(offset)) if offset
+        self
+      end
+
       def order(*expr)
         @ast.orders = expr
         self

activerecord/lib/arel/visitors/mysql.rb

@@ -56,18 +56,6 @@ module Arel # :nodoc: all
           super
         end
 
-        def visit_Arel_Nodes_UpdateStatement(o, collector)
-          collector << "UPDATE "
-          collector = visit o.relation, collector
-
-          unless o.values.empty?
-            collector << " SET "
-            collector = inject_join o.values, collector, ", "
-          end
-
-          collect_where_for(o, collector)
-        end
-
         def visit_Arel_Nodes_Concat(o, collector)
           collector << " CONCAT("
           visit o.left, collector
@@ -77,7 +65,23 @@ module Arel # :nodoc: all
           collector
         end
 
+        def build_subselect(key, o)
+          subselect = super
+
+          # Materialize subquery by adding distinct
+          # to work with MySQL 5.7.6 which sets optimizer_switch='derived_merge=on'
+          subselect.distinct unless subselect.limit || subselect.offset || subselect.orders.any?
+
+          Nodes::SelectStatement.new.tap do |stmt|
+            core = stmt.cores.last
+            core.froms = Nodes::Grouping.new(subselect).as("__active_record_temp")
+            core.projections = [Arel.sql(quote_column_name(key.name))]
+          end
+        end
+
         def collect_where_for(o, collector)
+          return super if o.offset
+
           unless o.wheres.empty?
             collector << " WHERE "
             collector = inject_join o.wheres, collector, " AND "

activerecord/lib/arel/visitors/to_sql.rb

@@ -88,6 +88,7 @@ module Arel # :nodoc: all
           core.wheres      = o.wheres
           core.projections = [key]
           stmt.limit       = o.limit
+          stmt.offset      = o.offset
           stmt.orders      = o.orders
           stmt
         end
@@ -800,7 +801,7 @@ module Arel # :nodoc: all
         end
 
         def collect_where_for(o, collector)
-          if o.orders.empty? && o.limit.nil?
+          if o.orders.empty? && o.limit.nil? && o.offset.nil?
             wheres = o.wheres
           else
             wheres = [Nodes::In.new(o.key, [build_subselect(o.key, o)])]