PostgreSQL SyntaxLesson 23Free preview

PostgreSQL COUNT

This lesson is part of PostgreSQL · All levels

Summary

COUNT is an aggregate function for calculating the number of rows or the number of values in a column. The COUNT(*) variants count all rows, whereas COUNT(column) only counts values that are not NULL. Plus DISTINCT, you can calculate how many unique values there are on that column.

Key points

COUNT(*) counts the entire row including the value of NULL.
COUNT(column) only counts the non-NULL value on that column.
COUNT(DISTINCT column) calculates the number of unique values.
It is often used together with GROUP BY for group statistics.

Full lesson

Code examples and quizzes

Full lessons, code examples, and quizzes are available to subscribers. 5 questions.