A User-Defined Function returns more rows

The Problem Recently, while working with one of my clients, I came across a script in which I had to introduce a scalar User-Defined Function in the SELECT statement. The SELECT used to return around 750K records. However, after introducing the UDF, the row count significantly increased to 826K. There were no other changes made […]

Performance of GROUP BY multiple columns

Grouping

Performance Surprises and Assumptions : GROUP BY vs. DISTINCT

Aaron Bertrand acknowledges that DISTINCT and GROUP BY are usually interchangeable, but shows there are cases where one performs better than the other.

Bones of SQL – Grouping By User-Defined Calendar Periods

Although it is common to group by periods such as Week, Month, or Quarter, sometimes alternative periods are needed. This simple technique lets you split a year into periods with any number of days.

More GROUP BY

SQL GROUP BY Basics

It sometimes pays to go back and look at what you think you already know about SQL. Joe Celko gives a quick revision of the GROUP BY and HAVING clauses in SQL that are the bedrock of any sort of analysis of data, and comes up with some nuggets that may not be entirely obvious.

Using the ROLLUP, CUBE, and GROUPING SETS Operators

Greg Larsen discusses the ROLLUP, CUBE and GROUPING SETS operators. These operators are used with the GROUP BY clause and allow you to create subtotals, grand totals and superset of subtotals. Read on to find out more about these additional GROUP BY operators.

Using SQL Server's GROUP BY clause to Summarize your Data

SQL Server’s GROUP BY clause provides you a way to aggregate your SQL Server data and to group data on a single column, multiple columns, or even expressions. Greg Larsen discusses how to use the GROUP by clause to summarize your data.

Group By, Count, and NULLs