How to remove duplicate records with out sort

Can any one give me command How to delete duplicate records with out sort.

Suppose if the records like below:

345,bcd,789
123,abc,456
234,abc,456
712,bcd,789

out tput should be
345,bcd,789
123,abc,456

Key for the records is 2nd and 3rd fields.fields are seperated by colon(,).

Try this:

nawk -F',' '!x[$2$3]++' input_file

It's working