In openerp 7 char data type float value stored. In list view sorting value how to change the char to float ?

In SQL Editor the below code is used:-

select char_value from cvw_patientintake order by cast(char_value as float) asc

select char_value from cvw_patientintake order by cast(char_value as float) desc

The above code how to apply in openerp custom module overriden search function is any sample code available?

Thanks in advance