Tricky query for multiple select of cobol variables in db2

I have a problem in Query when used with cobol and db2 as below

we are getting list of country codes which is character( 3) from file.
The country codes are seperated by commas(,).. This will vary each time. It can be 3 country codes or 24 country codes...etc

e.g IND,CHN,VEN


we have to write a query which will select student id's based on the country codes.

TABLE NAME STUDENT

COLUMNS : NAME( NAME OF STUDENT) ,STUDID( STUDENT IDENTIFICATION NUMBER),CTRY_CODE( COUNTRY CODES).


I have moved "IND,CHN,VEN" which is got from file to temporary variable. ws-parm-ctry

and using the query

select STUDID, NAME from STUDENT where CTRY_CODE in (:ws-parm-ctry).

some how this doesnt work. pls do suggest me some solution.