SQL GROUP BY Guide - Essential SQL

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

An overview of the SQL GROUP BY clause

GROUP BY SQL query to get number of records, average , maximum minimum & sum over a group of records

Group Rows and Get Counts Using Power Query | MyExcelOnline

GROUP BY SQL Queries to Summarize and Rollup Sets of Records

SQL PARTITION BY Clause overview