Explain what the ISNULL and NULLIF functions do.

IsNull Just Boolean NULLIF With Exeption

ISNULL Function Purpose: Replaces NULL values with a specified replacement value. Example: Imagine a table named Products with a column Discount that may contain NULL values. To handle these NULL values gracefully in a query, you can use ISNULL to ensure all output values are non-null. SELECT ProductName, ISNULL(Discount, 0) AS EffectiveDiscount FROM Products; NULLIF Function Purpose: Returns NULL if two given expressions are equal; otherwise, returns the first expression. This is particularly useful for avoiding errors in calculations. Example: Consider a table named Sales with columns TotalSales and NumberOfTransactions. To avoid division by zero when calculating the average sale per transaction, use NULLIF. SELECT TotalSales, NumberOfTransactions, TotalSales / NULLIF(NumberOfTransactions, 0) AS AvgSalePerTransaction FROM Sales; COALESCE Function In modern SQL environments, while ISNULL and NULLIF remain fundamentally the same, there's a broader acceptance and usage of more universally supported functions like COALESCE which is similar to ISNULL but can handle multiple parameters. COALESCE returns the first non-null value in a list of parameters. SELECT ProductName, COALESCE(Discount, 5) AS EffectiveDiscount FROM Products;