Final answer:
The keywords 'NULLS LAST' can be used in an ORDER BY clause to ensure NULL values are listed last in the results of an SQL query. This is useful for prioritizing non-null values in sorted data.
Step-by-step explanation:
The NULLS LAST keywords can be included in an ORDER BY clause to indicate that NULL values should be listed last in the results. When writing SQL queries, specifying the order in which rows are returned is often necessary, especially when dealing with reporting or data analysis tasks where the sequence of data matters. The ORDER BY clause is used to sort the data, and by default, NULL values are considered lower than any non-null value. Therefore, they appear first when sorting in ascending order and last when sorting in descending order. However, if you want to override this default behavior and deliberately position NULLs at the end of the result set regardless of the sorting order, you can use the NULLS LAST option. Here's an example of how to use NULLS LAST in a query:
SELECT column_name FROM table_name ORDER BY column_name ASC NULLS LAST;
This query will return all rows from the table, sorted by the selected column in ascending order, with NULL values appearing after all non-null values. The NULLS LAST keyword is particularly useful when you want to ensure that meaningful data appears first, leaving all undefined or missing values at the bottom of the result set.