• In SQL Server, the ISNULL( ) function is used to replace NULL value with another value.
• ISNULL( ) function is available in both SQL Server and MySQL even though they are different.
• For example, if we have the following table,

Table Wikitechy_Sales_Data

Store_Name	Sales
Store A	300
Store B	NULL

• The following SQL,

SELECT SUM (ISNULL(Sales,100)) FROM Wikitechy_Sales_Data;

• Returns the following result:

SUM (ISNULL(Sales,100))	
400	

• This is because NULL has been replaced by 100 via the ISNULL function, so the total becomes 300 + 100 = 400.

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MySQL:

• 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.

• For example,
• ISNULL(3*3) returns 0
• ISNULL(3/0) returns 1

SQL isnull VS is not null

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