Hi,
this equation is suficient; join is not really necessary, because P2 is single punch.
{P2=if(count(P1_1, P1_2, P1_3) == 1 AND P1_1 == 'Y', 1, if(count(P1_1, P1_2, P1_3) == 1 AND P1_2 == 'Y', 2, if(count(P1_1, P1_2, P1_3) == 1 AND P1_3 == 'Y', 3,
P2)))}
If you don't set the P2 here you will empty P2 in case you have more than one anwer in P1.
See example.
Regards
Joffm