9 Summarizing Data

Question 1

What is an aggregate function

Answer 1

A way to summarize data without actually retrieving it. Operates on a set of rows to calculate and return a single value

Question 2

Example of aggregate functions

Answer 2

-AVG(columnName)
-COUNT(columnName) or ()
-MIN(columnName)
-MAX(columnName)
-SUM(columnName*)

Question 3

What’s the difference between COUNT(columnName) and COUNT(*)

Answer 3

COUNT(*) counts ALL the rows in a table (includes values and NULL)

COUNT(columnName) counts ONLY the number of rows in that column with a value (ignores NULL)