turns out that Select takes an SqlExpression as a parameter. and inside the SqlExpression, the query can be built using Sql Syntax.
example:
SqlExpression<T> expression = new MySqlExpression<T>();
expression.WhereExpression = (whereExp.Length > 0 ? "WHERE " + whereExp : "");
expression.OrderByExpression = (orderExp.Length > 0 ? "ORDER BY " + orderExp : "");
expression = expression.Limit(skip: _pageIndex * _pageSize, rows: _pageSize);