Subtract values in same column from 2 different dates in same Mysql table
SELECT t1.item, t2.likes - t1.likes difference
FROM table t1, table t2
WHERE t1.item = t2.item
  AND t1.date = @first_date
  AND t2.date = @second_date


If you need all items (ever the data on @first_date or @second_date is not present), rewrite from cartesian to FULL JOIN and use COALESCE to replace NULLs with zeros.