where clause works woth raw int value but not with query sring's value

i am stroing a query string value in variable i.e.
int qryStrng_advId = int.Parse( Request.QueryString["advId"]);

and putting qryStrng_advId in where clause of select statement i.e.
String sqlQuery = "select advtitle,advDetails from tblJobAdv where advId = qryStrng_advId" ;

...