An overview of the SQL GROUP BY clause

How to do a group by clause

How to UPDATE from a SELECT statement in SQL Server

Overview of SQL COUNT and COUNT_BIG in SQL Server

Number of records in a table with different conditions by using SQL count() in less than 2 minutes

SQL Server COUNT() Function Performance Comparison

SQL GROUP BY Guide - Essential SQL

Group By in SQL Server with CUBE, ROLLUP and GROUPING SETS Examples

GROUP BY SQL Queries to Summarize and Rollup Sets of Records