So far, we’ve only considered changes in whole rows. What if only certain columns are changing? For example, what if in the Revised table, for some customer id, the name or phone number changed? It would be great to be able to report the rows that changed and also to provide a summary of the number of changes by column and also some way to see what changed between two rows, not just visually, but programmatically. These sample tables are small and narrow. Imagine a table with 40 columns, not 4 and 1 million rows, not 10. Computing such a summary would be very tedious. I’m thinking about something like this: