If you are comparing two tables with similar columns, something like a transactional table versus a staging table, then perhaps you can add to both tables a persisted computed column derived from a CHECKSUM of the column list. Once done, add index on PID + the checksum column. If my assumption is correct, the join operation could potentially be covered by this 2 column index, which would be very efficient.

create table MYTable

(

pid int not null,

a int null, b int null, c int null,

xupdate as checksum( a, b, c) persisted

);

create index ix_pid_xupdate on MYTable ( pid, xupdate );