In query examinations it is often interesting which columns query needs to access to provide result set as it gives you ideas if you can use covering indexes to speed things up or even cache some data by denormalizing tables. So far it has to be done manually – look at SELECT clause, WHERE clause, ORDER BY GROUP BY and HAVING to sum it up, not to mention more complex questions of subselects.
It would be great tool for MySQL Performance Optimization if MySQL Server could show this table and I know it already has this data as it is used by the optimizer.
It would be also good if such tool would show mapping of WHERE clauses to the tables as well as other clauses such as GROUP BY and ORDER BY. For complex queries especially if they do not refer to the columns with table prefix it may take a while to figure our where these columns come from and so how they can be optimized.