COUNT, SUM & AVG

Understand

The support table has one row per ticket, and nobody wants to read eight rows. They want a number: how many tickets, how long they took, how happy people were. COUNT, SUM and AVG each collapse a column into a single answer. The catch is what they do with the rows where the value is missing, and that is where most wrong answers in this lesson come from.

SELECT COUNT(*), SUM(which_column), AVG(which_column)
FROM where_it_lives
WHERE which_rows_to_include;