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← Aggregations - Intro to Relational Databases

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Showing Revision 4 created 05/25/2016 by Udacity Robot.

  1. So in the last quiz,
    you saw one example of an aggregation,
  2. a database operation that summarises
    multiple rows into a single row.
  3. Counting up the number of
    gorillas in the animals table,
  4. was a count aggregation.
  5. It takes several rows,
    each representing one gorilla, and
  6. turns them into one gorilla
    representing the count.
  7. Any time we want to compute a single
    result from a set of values,
  8. that's an aggregation.
  9. Here are some of the most common
    aggregation functions in SQL.
  10. Count is different from the other ones,
    in that it takes values of any type, and
  11. returns a number.
  12. Most of the other aggregations
    only work on numbers.
  13. For instance, you can't the average
    of a column of string values,
  14. because only numbers have an average.
  15. We'll see a lot more about
    aggregations in the next lesson.