1 files changed, 87 insertions, 0 deletions
diff --git a/activerecord/lib/arel/visitors/mysql.rb b/activerecord/lib/arel/visitors/mysql.rb
new file mode 100644
index 0000000000..37bfb661f0
--- /dev/null
+++ b/activerecord/lib/arel/visitors/mysql.rb
@@ -0,0 +1,87 @@
+# frozen_string_literal: true
+
+module Arel # :nodoc: all
+  module Visitors
+    class MySQL < Arel::Visitors::ToSql
+      private
+        def visit_Arel_Nodes_Union(o, collector, suppress_parens = false)
+          unless suppress_parens
+            collector << "( "
+          end
+
+          collector =   case o.left
+                        when Arel::Nodes::Union
+                          visit_Arel_Nodes_Union o.left, collector, true
+                        else
+                          visit o.left, collector
+          end
+
+          collector << " UNION "
+
+          collector =    case o.right
+                         when Arel::Nodes::Union
+                           visit_Arel_Nodes_Union o.right, collector, true
+                         else
+                           visit o.right, collector
+          end
+
+          if suppress_parens
+            collector
+          else
+            collector << " )"
+          end
+        end
+
+        def visit_Arel_Nodes_Bin(o, collector)
+          collector << "BINARY "
+          visit o.expr, collector
+        end
+
+        ###
+        # :'(
+        # http://dev.mysql.com/doc/refman/5.0/en/select.html#id3482214
+        def visit_Arel_Nodes_SelectStatement(o, collector)
+          if o.offset && !o.limit
+            o.limit = Arel::Nodes::Limit.new(18446744073709551615)
+          end
+          super
+        end
+
+        def visit_Arel_Nodes_SelectCore(o, collector)
+          o.froms ||= Arel.sql("DUAL")
+          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
+
+          unless o.wheres.empty?
+            collector << " WHERE "
+            collector = inject_join o.wheres, collector, " AND "
+          end
+
+          unless o.orders.empty?
+            collector << " ORDER BY "
+            collector = inject_join o.orders, collector, ", "
+          end
+
+          maybe_visit o.limit, collector
+        end
+
+        def visit_Arel_Nodes_Concat(o, collector)
+          collector << " CONCAT("
+          visit o.left, collector
+          collector << ", "
+          visit o.right, collector
+          collector << ") "
+          collector
+        end
+    end
+  end
+end