Does “group by” automatically guarantee “order by”?

Question

Does \"group by\" clause automatically guarantee that the results will be ordered by that key? In other words, is it enough to write:

select * 
from table
group          


        

Answer 1

I tried it. Adventureworks db of Msdn.

select HireDate, min(JobTitle)
from AdventureWorks2016CTP3.HumanResources.Employee
group by HireDate

Resuts :

2009-01-10Production Technician - WC40

2009-01-11Application Specialist

2009-01-12Assistant to the Chief Financial Officer

2009-01-13Production Technician - WC50<

It returns sorted data of hiredate, but you don't rely on GROUP BY to SORT under any circumstances.

for example; indexes can change this sorted data.

I added following index (hiredate, jobtitle)

CREATE NONCLUSTERED INDEX NonClusturedIndex_Jobtitle_hireddate ON [HumanResources].[Employee]
(
    [JobTitle] ASC,
    [HireDate] ASC
)

Result will change with same select query;

2006-06-30 Production Technician - WC60

2007-01-26 Marketing Assistant

2007-11-11 Engineering Manager

2007-12-05 Senior Tool Designer

2007-12-11 Tool Designer

2007-12-20 Marketing Manager

2007-12-26 Production Supervisor - WC60

You can download Adventureworks2016 at the following address

https://www.microsoft.com/en-us/download/details.aspx?id=49502