Replace query

I have a file with 3 columns as below

column1      column2         column3
1,           corporate,unix,      2300
2,           business,unix,    23000

I need to replace "," with "|" as delimiter but the problem is the second column already has comma which is also getting replaced. I need to replace "," to separate 3 columns alone.

PLEASE HELP

Like this???

sed 's/, / | /g' infile

Sorry to be precise my input files looks like below

column1      column2         column3
1,corporate,unix,2300
2,business,unix,23000

no space between the columns.. Soory for inconvenience

sed -e 's/,/|/g' infile -e 's/|/,/2'

sed -e 's/,/|/1' -e 's/,/|/2' infile