How to Take SQL INNER JOIN Basic Question One Step Further

Instead of SELECT * FROM patrons which selects all columns from patrons you'll want to select the individual columns that you desire. Also, you'll use an alias to specify the file names.

Something like:

SELECT a.col1, a.col2, b.colx, b.coly FROM patrons INNER JOIN loans as b .... (you can still use a.* to select all columns).

Go to SQL Fiddle and experiment.

Also, it would probably be worth your time to load MySQL on your local machine. There are many options depending on your OS.

I used the LEFT OUTER JOIN with patron as the left sided table. A rough Venn diagram can show clearly that table patrons and books are completely distinct from each other but both join the loans table on patron-id on the left side and book-id on the right side. In addition, loans table has its own independent columns.

[SELECT first_name, email, return_by, return_on, loaned_on FROM patrons LEFT OUTER JOIN loans ON patrons.id = loans.patron_id WHERE loans.returned_on IS NULL AND loans.return_by < DATE("now");]

I added the third (return_by) and fourth (return_on) columns simply to prove whether my answer made sense. I could not use DISTINCT because at any one time a single patron can have more that one outstanding books and yet I need to identify each of outstanding books individually. The correct columns to select therefore are according to the question, first name and email but I even added the column issued_on and clearly the returned on column is all blank because these books are still outstanding to date. I avoided aliasing unnecessarily as this would rather appear cluttering my code although in complex queries this would have been necessary.

Err: replace issued on with loaned_on