SQL · Aggregation and grouping

count()

count(*) counts rows; count(column) ignores NULLs.

sqlRunnable example sql course

Syntax

count(*) / count(column)

Example

Open in the lab

WITH lessons(note) AS (VALUES (NULL), ('a'), ('b'))
SELECT count(*) AS rows, count(note) AS with_note FROM lessons;

Reference pages are the quick answer. The course explains the why, shows the full example and ends with a challenge.