I have often seen T-SQL beginners having confusion over the sequence and usage of GroupBy, Having and Order By clause. Here’s a simple example:
I am using the AdventureWorks database.
SELECT CustomerID, SUM(TaxAmt) AS CustomerTax
GROUP BY CustomerID
HAVING SUM(TaxAmt) > 2000
ORDER BY CustomerID
As you can see, we are using HAVING to filter rows based on an aggregate expression. Note that you can include nonaggregate columns in the HAVING clause, however the condition is that these columns must appear in the GROUP BY clause.
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