Working with NULL values
A NULL value could mean 'zero' - if something doesn't happen, it can't be logged in a table. However, NULL can also mean 'unknown' or 'missing'. So consider if it is appropriate to replace them in your results. NULL values provide feedback on data quality. If you have NULL values, and you didn't expect to have any, then you have an issue with either how data is captured or how it's entered in the database.
In this exercise, you'll practice filtering for NULL values, excluding them from results, and replacing them with alternative values.
Deze oefening maakt deel uit van de cursus
Introduction to SQL Server
Praktische interactieve oefening
Probeer deze oefening eens door deze voorbeeldcode in te vullen.
-- Retrieve all columns
SELECT
___
FROM
grid
-- Return only rows where demand_loss_mw is missing or unknown
WHERE
___ ___ ___;