IS NULL and
IS NOT NULL are used in
WHEREclauses to 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
outcome_type that 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:
An introduction to the
NOT LIKE keywords.