Okay, let’s get our act together. To find out if a cell is NULL why not just ask…ISNULL? Well, yes, this does work for mySQL. But it isn’t that simple. What if we wanted an easy way to replace the null value with something else? Good idea you say. So the powers that be at mySQL came up with IFNULL(). It looks like this:
SELECT IFNULL(column1, “alternative”) FROM table
So if the expression in column1 turns out to be NULL you can make it something else.
Where it gets a bit confusing is that some applications use ISNULL() the way mySQL uses IFNULL(). And some use a completely different syntax. NVL() is how it looks in Oracle.
But there is another way of doing this available in most applications. It is called COALESCE(). This looks alot like IFNULL (mySQL) but has the added feature that it can take multiple parameters and will in the end return the first one that it finds that is NOT NULL. So you can do something like this:
SELECT COALESCE(column1, column2, etc., “alternative”) FROM table
This will return the first not null param that it runs across. Leave the failsafe for the end.
