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GROUP BY Extensions in SQL

Introduction
CUBE
Summary

Instruction

Great! Lastly, the function COALESCE() can be used in the SELECT clause to replace NULL values with the values of your choice:

SELECT
  COALESCE(location, '--') AS location,
  COALESCE(gender, '--') AS gender,
  COALESCE(risk, '--') AS risk,
  AVG(age) AS avg_age
FROM vaccine_administration
GROUP BY 
  CUBE (location, gender, risk);

In the query above, '--' will be shown when location, gender, or risk is NULL.

Exercise

Run the template query and note how NULLs are replaced with '--'.