Question

I am trying to run through a program to check if vouchers are valid within a vouchers table.

There are some simple validation aspect such as whether the voucher has passed expiry date or not, but also, some vouchers might be conditional based upon a customer buying specific products by brand, or supplier.

So, I have table of vouchers

    id    |     brand     |     supplier    |    value    etc

a table of brands

   id     |      name       etc

and a table of suppliers

   id     |     name     etc

If a voucher is not specific to a brand or supplier, then the value in the vouchers tale is 0

I have tried this Sql query inner joining the tables, but I get no results, I am assuming this is because the voucher code (id) I am trying to use is not specific to a brand or supplier?

SELECT *, brands.name as brandName, suppliers.name as supplierName  
    FROM `vouchers` 
    INNER JOIN brands on vouchers.brand = brands.id 
    INNER JOIN suppliers on vouchers.supplier = suppliers.id 
    WHERE vouchers.id= '" & voucherCode & "'

How would I write this so that the joining of the table brands is conditional upon the value brand in the table vouchers is greater than 0 (and then simiarly for suppliers)

I have had a look on here and see several other questions posted, but I am afraid I don’t fully understand the answers to e able to relate them to my situation.

Using MySQL database by the way 🙂

Answer 1

Why don’t you just do a LEFT JOIN instead like this:

SELECT *, brands.name as brandName, suppliers.name as supplierName  
    FROM `vouchers` 
    LEFT JOIN brands on vouchers.brand = brands.id 
    LEFT JOIN suppliers on vouchers.supplier = suppliers.id 
    WHERE vouchers.id= '" & voucherCode & "'

This will return all the vouchers no matter if they have brands or suppliers