Treat NULL as Zero 0 before Incrementing Column value by 1 - SQL Server

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Let's imagine you have an online quiz application where users answer multiple-choice questions. In this scenario, you want to keep track of how many times each question has been attempted by users. However, you encounter a situation where some number_of_attempts column values in the Quiz table are initially set to NULL instead of 0.

Let us assume, I have table name "dbo.Quiz" with columns "qid", "question" and "number_of_attempts". Some questions have never been attempted before, so their "number_of_attempts" value is NULL. I want to update the "number_of_attempts" value for specific questions every time they are attempted.

Here's the SQL query.

UPDATE dbo.Quiz
SET number_of_attempts = COALESCE(number_of_attempts, 0) + 1
WHERE QID IN (2, 3, 9);

If the "number_of_attempts" value for a question is NULL, it is treated as 0 and incremented to 1. However, if the number_of_attempts value is already a number, it is simply incremented by 1.

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COALESCE() function in SQL Server

The COALESCE() function in SQL Server is useful when dealing with NULL values.

Syntax:

COALESCE(expression1, expression2, ..., expressionN)

COALESCE takes multiple expressions and returns the first non-NULL expression from the list.

See this example

1) COALESCE allows you to substitute NULL values with a specified default value. This is especially useful when you want to avoid NULL values in your results or computations.

2) By using COALESCE, you can maintain data integrity and avoid unexpected results caused by NULL values. It helps ensure that your queries and calculations return meaningful and accurate results.

3) COALESCE makes your SQL queries more readable and easier to understand. Instead of writing complex CASE statements or using multiple IS NULL checks, you can achieve the same result with a simple and clear COALESCE function.

4) This is important: COALESCE can take multiple arguments and returns the first non-NULL value from the list. This makes it versatile for handling multiple possible NULL values in your data.

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