It has been a while since we have seen a puzzle so let us do a small puzzle today. Actually, this is a very simple puzzle if you have worked with SQL Server for a while. I got an email from one of the readers from the blog post and he wanted me to correct the following query which he had written. Well, I have been working with SQL Server for over 19 years and I often do not remember the syntax and have to look up online. Here is a very simple puzzle for you which involves Aggregate and Subquery.
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Puzzle – Aggregate and Subquery
Here is the query when we run against the AdventureWorks database, it gives us an error. Remember AdventureWorks database is a sample database and you can download and install AdventureWorks over here.
USE AdventureWorks2014 GO SELECT pch.StandardCost, p.ProductID FROM Production.ProductCostHistory pch INNER JOIN Production.Product p ON pch.ProductID = p.ProductID WHERE pch.StandardCost > AVG(p.StandardCost) GO
Now when you run the above query, it gives us the following error:
Msg 147, Level 15, State 1, Line 17
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.
Now here is your task, you need to help me to fix the above query. The hint to resolve the query is already in the blog post’s title and in the query error. You need to understand what my query is attempting to do and use the hint which is already pointed out to you. After you successfully fix the query it will produce the following results.
Well, there are no real rules, as long as you modify my query to get me above results. Please post your query in the comments section below before April 22, 2019. I will keep all the answers hidden till April 22, 2019 11:59:00 PM.
One Winner will get 1 free seat for my upcoming class, which is worth USD 1000.
SQL Server Performance Tuning Practical Workshop for EVERYONE
Date: April 23, 2019, Tuesday
8:00 AM Pacific Time | 11:00 AM Eastern Time
If you do not want to take part in the contest, you can directly register for the class here.
Update: April 23, 2019
The contest is closed and the winning Answer is here:
USE AdventureWorks2014 GO SELECT pch.ProductID, pch.StartDate,pch.EndDate, pch.StandardCost, pch.ModifiedDate FROM Production.ProductCostHistory pch INNER JOIN Production.Product p ON pch.ProductID = p.ProductID WHERE pch.StandardCost > p.StandardCost GO
There is no need for the AVG on the StandardCost as there will be always a single entry for the product. Even if you change the query with group by + having you will still see the query uses the simple join.
Congratulations to the winner Nicholas Månsson. He is very excited to join the SQL Server Performance Tuning Practical Workshop for EVERYONE.
Everyone who participated you got to solve this difficult puzzle so indirectly you are a winner (of knowledge) as well. This was an intense competition with over 500 comments.
Reference: Pinal Dave (https://blog.sqlauthority.com)