SQL Sorting Hacks: Prioritize or Push Null Dates Back in Results

Using CASE expression:

This method uses a CASE expression to assign a value depending on whether the date is null or not. We then sort by this assigned value first (in descending order) and then by the actual date (also in descending order).

SELECT *
FROM your_table
ORDER BY CASE WHEN your_date_field IS NULL THEN 1 ELSE 0 END DESC,
         your_date_field DESC;

Explanation:

• CASE: This checks if the your_date_field is null.
  • If null, it assigns 1.
• ORDER BY:
  • We first sort by the result of the CASE expression in descending order (DESC). This places null values (assigned 1) at the top.
  • Then, we sort by the actual your_date_field also in descending order, ensuring proper date sorting within non-null values.

Using COALESCE function:

This method utilizes the COALESCE function, which replaces null values with a specified value. We use '9999-12-31' (a very late date) as a placeholder for nulls.

SELECT *
FROM your_table
ORDER BY COALESCE(your_date_field, '9999-12-31') DESC;

• COALESCE(your_date_field, '9999-12-31'): This replaces null values in your_date_field with the string '9999-12-31'.
• ORDER BY: We sort by the result of the COALESCE function in descending order. Since null values are replaced with a very late date, they effectively appear at the end.

Related Issues:

• Database-specific functions: Some databases offer functions like ISNULL for null checks. However, it's recommended to use CASE or COALESCE for wider compatibility across different SQL dialects.
• Performance: The CASE and COALESCE methods might have slightly different performance implications depending on the database and data size. Benchmarking might be necessary for large datasets.