IS NULL and
IS NOT NULL are used in
either display rows for which there is no value in a specified column or to
show only those rows which have a value in the specified column.
In the outcome table of our dataset there is the column
contains the different outcomes for the animals at the center. Some of the
possible outcomes are further defined by subtypes captured in the
outcome_subtype field. If we wanted to return only data that has both an
outcome type and an outcome subtype we could write the query thus:
SELECT monthyear, animal_type, outcome_type, outcome_subtype FROM austin_animal_center_outcomes WHERE outcome_subtype IS NOT NULL
and the first several rows returned would look like this:
Exercises (Continued from previous section)
There are two ways to do these exercises. You can use the “Try query” links to test your queries without saving them, or you can create a data.world project and save your queries to it. If you are reading this documentation and completing the exercises as a tutorial, you will need to create your own project to save your work. Details and instructions are in SQL tutorial which has instructions for setting up your project and links to all the current exercises.
Using the patient, description, and reasondescription columns from the medications table, write a query that returns the records where reasondescription is not null.
SELECT the columns
IS NOT NULL.
An introduction to the
NOT LIKE keywords.