Question

There is a VARCHAR2 type column in my database table for store invoice_number. and there is a query to get max invoice_number as below.

select max(invoice_number)  from invoice;

but there are no data in invoice table, above query return value as null. but in this case i need to replace this value to 0 instead of null. how could i do this ?

Answer 1

Using NVL:

SELECT NVL(MAX(invoice_number), '0')

Using the ANSI COALESCE:

SELECT COALESCE(MAX(invoice_number), '0')

Using DECODE:

SELECT DECODE(MAX(invoice_number), NULL, '0')   

Using the ANSI CASE:

SELECT CASE 
         WHEN MAX(invoice_number) IS NULL THEN '0' 
         ELSE MAX(invoice_number) 
       END

Verdict

All work, I’d probably use NVL because COALESCE is ANSI but not known to necessarily work as fast as native alternatives.