Dear Monks

What started as a simple exercise, has now gone beyond my (regex) knowledge.
I need to split the following on ',':

$part_sql = "f1,f2, SUM(f3),CONCAT(f4,f5, f6), f7"
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The problem is that I don't want to split the stuff inside the CONCAT.
Firts I thought that it was easy, like

my @fields = split(/(?<!\([^\)]+),/, $part_sql);
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This raised the following error

Variable length lookbehind not implemented in regex; marked by <-- HER
+E in m/(?<!\([^\)]+), <-- HERE / ....
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Is there a regex that can do this, or should I do it just differently ?

Cheers
LuCa

Update: from the answers I get the impression that a SQL-parser-module would be the best solution, but for now I choose the quick solution provided by martin.
Thnx for all the suggestion!!