How to include only null values in an Expression

[sriddell]

Hi, 

I'm looking for help with an expression in a straight table. 

I have a field called 'fordel' where some returns are = 1 and others are null. I then have a field which I wish to sum the values of, and that field is called 'enrol'.

I wish to display results only where fordel is not equal to 1, i.e. the null values. I've tried the below without success - I'd appreciate any advice. 

sum({$<fordel-={'1'}>},(enrol)

Best wishes. 

[maxgro · Accepted solution]

maybe

Sum({$-<[fordel={'*'}>} enrol)

or you can replace the null in fordel field with 0 in the load script and then 

sum({$<fordel={0}>} enrol)

[sriddell]

Thank you very much, Maxgro - the first solution worked perfectly (and I can understand why the second one would too). I really appreciate your advice here.