I have got a dataset like this
email@example.com,2009-11-27 firstname.lastname@example.org,2009-11-27 email@example.com,2009-11-27
When I am running command to delete all of the same entries of column2
sort -t ',' -k2 stars.txt -u
It is deleting the entry of column1.
In order to delete the duplicate entries of column2, I am having to enter
sort -t ',' -k3 stars.txt -u
Can anyone explain to me why it is happening? Why I have to enter +1 to the column in the file to delete the column?