Aggregates and GROUP BY - PostgreSQL for Developers
Aggregates and GROUP BY - part of PostgreSQL for Developers.
PostgreSQL from the inside out - fundamentals through internals and ops.
In this lesson:
Every non-aggregated SELECT column must appear in GROUP BY — Postgres errors if not, but check MySQL-ported code carefully
HAVING belongs after GROUP BY and references aggregates; if the condition references a plain column with no aggregate, it probably belongs in WHERE
COUNT(*) counts all rows including NULLs; COUNT(col) counts only non-NULL values — verify the intent matches the column chosen
Chapters:
0:00 Intro
0:13 What Aggregates and GROUP BY Do
0:27 Walkthrough
0:41 Walkthrough
0:59 Under the Hood: Rows In, Groups Out
1:16 Live Example: Revenue by Customer
1:39 Review Lens: Non-Aggregated Column Missing from GROUP BY
1:57 Recap
Module: SQL Fundamentals
Every command and code example in this video is executed and verified before publishing.
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