Working with NULL values in SQL is an important aspect of handling missing or unknown data in a database. NULL represents the absence of a value and is not the same as an empty string or zero. Understanding how NULL behaves in SQL queries and how to work with it is crucial for accurate data analysis and manipulation.

1. NULL Comparison:
   • Comparing a value to NULL using regular comparison operators (=, !=, <, >, <=, >=) doesn’t yield a true or false result. Instead, it results in an unknown result.
   • For example, NULL = 5 or NULL != 'hello' both result in NULL, not true or false.
2. IS NULL / IS NOT NULL:
   • To check if a column contains NULL values, you use the IS NULL condition.
   • To check if a column does not contain NULL values, you use the IS NOT NULL condition.
3. Handling NULL Values in Functions:
   • Many functions in SQL ignore NULL values or treat them differently. For instance, SUM ignores NULL values, while COUNT counts them.
   • You can use the COALESCE function to replace NULL values with a specified default value.
4. Working with NULL in Joins:
   • When using joins, NULL values can affect how records are matched. INNER JOINs exclude NULL values, while LEFT and RIGHT JOINs include them based on which table contains NULL values.
5. Using NULL in INSERT and UPDATE:
   • You can explicitly insert NULL values into columns during an INSERT operation.
   • You can also use NULL in UPDATE statements to set columns to NULL.
6. Aggregate Functions and NULL:
   • Many aggregate functions, like SUM, AVG, and COUNT, treat NULL values differently. For example, COUNT includes NULL values in its count.
7. ORDER BY and NULL:
   • NULL values can affect sorting in ORDER BY clauses. By default, NULL values are usually sorted at the end of a result set.
8. CASE Statements with NULL:
   • You can use CASE statements to handle NULL values and create conditional expressions based on them.