The IFNULL() in SQL is basically used to replace null values with some other values. This function takes two arguments –
expression – The expression that you want test
alt_value – The value to return if expression is NULL
If you run the following code –
SELECT IFNULL(5, 0) -- return 5 SELECT IFNULL('LWD', 0) -- return LWD string
The first query will return 5 as 5 is not a null and the second query will return the string LWD as this is also not null.
But if the first expression is NULL
SELECT IFNULL(NULL, 0) -- return 0
Then it will return the second argument that is passed to the IFNULL function which is 0 in this case.