SQL - Handle NULL Values Safely in Queries

When working with SQL queries, be cautious when dealing with NULL values. Use SQL functions like IS NULL, IS NOT NULL, COALESCE, and CASE statements to handle NULL values appropriately, preventing unexpected results or errors in your queries.

Suppose you have a table called "employees" with a "birthdate" column that may contain NULL values, and you want to retrieve the age of each employee.

Dealing with NULL Values:

SELECT employee_id, 
       CASE
           WHEN birthdate IS NULL THEN 'N/A'
           ELSE DATE_DIFF(CURRENT_DATE(), birthdate) / 365
       END AS age
FROM employees;

In this example, the CASE statement checks if the "birthdate" is NULL, and if so, it returns 'N/A.' Otherwise, it calculates the employee's age using DATE_DIFF. This approach ensures that NULL values are handled gracefully, preventing potential errors or unexpected results in the age calculation.

Handling NULL values properly in your SQL queries is essential for accurate data processing and reporting. Use SQL's built-in functions and conditional statements to tailor your queries to the specific handling requirements of your data.