Build valid SQL query for SQLite3 and PostgreSQL when updating record…

…s with limited conditions

lib/arel/engines/sql/relations/writes.rb

@@ -24,8 +24,7 @@ def to_sql(formatter = nil)
       build_query \
         "UPDATE #{table_sql} SET",
         assignment_sql,
-        ("WHERE #{wheres.collect(&:to_sql).join('\n\tAND ')}"  unless wheres.blank? ),
-        ("LIMIT #{taken}"                                      unless taken.blank?  )
+        build_update_conditions_sql
     end
 
   protected
@@ -39,5 +38,22 @@ def assignment_sql
         assignments.value
       end
     end
+
+    def build_update_conditions_sql
+      conditions = ""
+      conditions << " WHERE #{wheres.collect(&:to_sql).join('\n\tAND ')}" unless wheres.blank?
+      conditions << " ORDER BY #{order_clauses.join(', ')}" unless orders.blank?
+
+      unless taken.blank?
+        conditions << " LIMIT #{taken}"
+
+        if engine.adapter_name != "MySQL"
+          quote_primary_key = engine.quote_column_name(table.name.classify.constantize.primary_key)
+          conditions =  "WHERE #{quote_primary_key} IN (SELECT #{quote_primary_key} FROM #{engine.connection.quote_table_name table.name} #{conditions})"
+        end
+      end
+
+      conditions
+    end
   end
 end

spec/arel/engines/sql/unit/relations/update_spec.rb

@@ -1,5 +1,11 @@
 require File.join(File.dirname(__FILE__), '..', '..', '..', '..', '..', 'spec_helper')
 
+class User
+  def self.primary_key
+    "id"
+  end
+end
+
 module Arel
   describe Update do
     before do
@@ -45,17 +51,17 @@ module Arel
 
         adapter_is :sqlite3 do
           sql.should be_like(%Q{
-            UPDATE "users"
-            SET "name" = 'nick'
-            LIMIT 1
+            UPDATE "users" SET
+            "name" = 'nick'
+            WHERE "id" IN (SELECT "id" FROM "users"  LIMIT 1)
           })
         end
 
         adapter_is :postgresql do
           sql.should be_like(%Q{
-            UPDATE "users"
-            SET "name" = E'nick'
-            LIMIT 1
+            UPDATE "users" SET
+            "name" = E'nick'
+            WHERE "id" IN (SELECT "id" FROM "users"  LIMIT 1)
           })
         end
       end