mysql selects from dual on empty from statements

3 files changed, 13 insertions, 1 deletions

diff --git a/lib/arel/visitors/mysql.rb b/lib/arel/visitors/mysql.rb
index 594fd5504a..afffd37f9b 100644
--- a/lib/arel/visitors/mysql.rb
+++ b/lib/arel/visitors/mysql.rb
@@ -10,6 +10,11 @@ module Arel
         super
       end
 
+      def visit_Arel_Nodes_SelectCore o
+        o.froms ||= Arel.sql('DUAL')
+        super
+      end
+
       def visit_Arel_Nodes_UpdateStatement o
         [
           "UPDATE #{visit o.relation}",
diff --git a/lib/arel/visitors/to_sql.rb b/lib/arel/visitors/to_sql.rb
index 1412797fb5..3c96b3e259 100644
--- a/lib/arel/visitors/to_sql.rb
+++ b/lib/arel/visitors/to_sql.rb
@@ -48,6 +48,7 @@ module Arel
           ("WHERE #{wheres.map { |x| visit x }.join ' AND '}" unless wheres.empty?)
         ].compact.join ' '
       end
+
       def visit_Arel_Nodes_InsertStatement o
         [
           "INSERT INTO #{visit o.relation}",
diff --git a/test/visitors/test_mysql.rb b/test/visitors/test_mysql.rb
index 1d38161caf..871d662d4b 100644
--- a/test/visitors/test_mysql.rb
+++ b/test/visitors/test_mysql.rb
@@ -14,7 +14,13 @@ module Arel
         stmt = Nodes::SelectStatement.new
         stmt.offset = Nodes::Offset.new(1)
         sql = @visitor.accept(stmt)
-        sql.must_be_like "SELECT LIMIT 18446744073709551615 OFFSET 1"
+        sql.must_be_like "SELECT FROM DUAL LIMIT 18446744073709551615 OFFSET 1"
+      end
+
+      it 'uses DUAL for empty from' do
+        stmt = Nodes::SelectStatement.new
+        sql = @visitor.accept(stmt)
+        sql.must_be_like "SELECT FROM DUAL"
       end
     end
   end