The ISNULL( ) function is available in both SQL Server and MySQL. However, their uses are different:
In SQL Server, the ISNULL( ) function is used to replace NULL value with another value.
For example, if we have the following table,
The following SQL,
SELECT SUM (ISNULL(Sales,100)) FROM Sales_Data;
returns the following result:
This is because NULL has been replaced by 100 via the ISNULL function, so the total becomes 300 + 100 = 400.
In MySQL, the ISNULL( ) function is used to test whether an expression is NULL. If the expression is NULL, this function returns 1. Otherwise, this function returns 0.
ISNULL(3*3) returns 0
ISNULL(3/0) returns 1
Next: SQL IFNULL Function
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