protected virtual Expression VisitAlterTable(AlterTableExpression node)
 {
     Append("ALTER TABLE");
     Visit(node.Table);
     Visit(node.Columns);
     Visit(node.Constraints);
     return(node);
 }
 protected virtual Expression VisitAlterTable(AlterTableExpression node)
 {
     Append("ALTER TABLE");
     Visit(node.Table);
     Visit(node.Columns);
     Visit(node.Constraints);
     return node;
 }