protected virtual Expression VisitCreateIndex(CreateIndexExpression node)
 {
     Append("CREATE");
     VisitIndexType(node.IndexType);
     Append("INDEX");
     Append(node.Name);
     Append("ON");
     Visit(node.Table);
     Append("(");
     Visit(node.Columns);
     Append(")", false);
     return node;
 }