Where .... and !isnull(f1)

>How can I keep the records where f1 is NULL from being included in result?
>
>

>testconnString = "Select webprddt6.resmngta0.recseq, webprddt6.resmngta0.jobno, webprddt6.resmngta1.schedtype," +;
>" Case When schedtype = 0 Then(Select SUM(taskdur) As tDur From webprddt6.resmngta3 Where schdindex = webprddt6.resmngta1.recseq And ftdatem > '09/01/2009')" +;
>" When schedtype = 1 Then(Select SUM(taskdur) As tDur From webprddt6.resmngta3d Where schdindex = webprddt6.resmngta1.recseq And ftdatem > '09/01/2009')" +;
>" End As f1" +;
>" From webprddt6.resmngta0" +;
>" Join webprddt6.resmngta1 On webprddt6.resmngta1.projindex = webprddt6.resmngta0.recseq" +;
>" Where status = 1 And deptno = '670' And projected = 0"
>