Hey,
I am wondering what it is the special field “$last” ?
Thanks
There’s no ‘special field’ called $last. You created a column called last, so you can refer to it in formulas. But if you refer to last in last, that’s a circular reference, i.e. last depends on itself and thus can’t be calculated.
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omg how silly am I 
I thought it was an existing special field because of the autocomplete , I forgot that I named it “last” 
by the way, is it the right way to fetch the last “data_created” column of a row from a $group :
$group.date_created[-1]
It’s best not to rely on the order of records in a group. Try MAX($group.date_created).
oki thanks
I tried it and voila the value I got : “01-01-1970 01:00:00”
which is false, what could be wrong , the both column have Datetime type
Does it mean that , there is some values in “date_created” with a wrong date ?
Ah, that’s because MAX ignores non-numeric values. Try using the Python builtin max instead, although this will require all the cells to be non-empty.
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thanks 
You are right, I didn’t read well the doc, my bad.
Function reference - Grist Help Center (getgrist.com)