input.sql

/* Given these SQL commands */
update books set author="Bob" where id=1;
update books set author="John" where id=2;
update books set author="Bob" where id=3;

output.sql

/* I want this output (and it should work with more complex scenarios) */
update books set author="Bob" where id in (1, 3);
update books set author="John" where id=2;