MS SQL tutorial on aggregate functions (COUNT, MIN, MAX, SUM AND AVG)

This is a SQL tutorial video on aggregate functions. Specifically COUNT, MIN, MAX, SUM AND AVG). This tutorial also includes GROUP BY, HAVING and ORDER BY.
This video shows how to write aggregate functions and the rules that need to be followed. It also looks at the following errors:

Error message discussed:
An aggregate may not appear in the WHERE clause unless it is in a subquery contained in a HAVING clause or a select list, and the column being aggregated is an outer reference.
Column is invalid in the select list because it is not contained in either an aggregate function or the GROUP BY clause.

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