Question

I’ve had a look around and have found example queries where the IF forms part of the record selection, but I want it to form part of what is output.

Basically I have a table of products which includes a manufacturer id and part id as well as a unique record number. Many of the products have a barcode, but not all. What I want to do is create a query to list all of the products, but where there is no barcode generate a barcode for internal use based on the unique record number. It doesn’t need to be a valid barcode for external purposes, so I’m not bothered about the check digit generation. I’ve done something similar in Excel years ago, but can’t work out how I do the IF bit in an SQL query. The following is an example of what I’d like to do, but the syntax isn’t right:

SELECT manufacturerID, partID, if(barcode is blank, "5000000"+unqueID, barcode)
FROM products

I’ve seen CASE statements mentioned, but couldn’t get my head around how it would fit in this example.

Answer 1

If you are just worried about null values, something like NVL (oracle) or ISNULL (mysql) can help

SELECT manufacturerID, partID, NVL(barcode, "5000000"+uniqueID) FROM products;

If your comparison is scalar, then decode can help as well

http://www.techonthenet.com/oracle/functions/decode.php

SELECT  manufacturerID, partID,
        DECODE (barcode, '',    5000000+uniqueID, barcode) result
FROM suppliers;

or finally you always have case, mother of all

select manufacturerID, partID,
    CASE 
         WHEN barcode = '' THEN "5000000" + uniqueID 
         ELSE barcode 
    END
from products