SQL Server: Distinct Count across Multiple Tables

One of my clients had a SQL Server database with an email column repeated across multiple tables. He wanted two queries – all email’s that are not repeated across the table, i.e. distinct ones as well as a count of the email addresses across multiple tables in the database.

I gave him a query that will help him out to do a count across multiple tables as well as list all distinct emails. Let us consider the following sample data

Now to do a count of email across multiple tables, use the following query:

SELECT tt.email, COUNT(tt.email) as EmailCount
FROM (  SELECT email FROM @t
        UNION ALL
        SELECT email FROM @t1) tt
GROUP BY tt.email

OUTPUT




Similarly to list all distinct email addresses, i.e the ones not repeated, use the HAVING clause (there are other ways too)

SELECT tt.email, COUNT(tt.email) as EmailCount
FROM (  SELECT email FROM @t
        UNION ALL
        SELECT email FROM @t1) tt
GROUP BY tt.email
HAVING COUNT(tt.email) = 1

About The Author

Suprotim Agarwal, MCSD, MCAD, MCDBA, MCSE, is the founder of DotNetCurry, DNC Magazine for Developers, SQLServerCurry and DevCurry. He has also authored a couple of books 51 Recipes using jQuery with ASP.NET Controls and a new one recently at The Absolutely Awesome jQuery CookBook.

Suprotim has received the prestigous Microsoft MVP award for nine times in a row now. In a professional capacity, he is the CEO of A2Z Knowledge Visuals Pvt Ltd, a digital group that represents premium web sites and digital publications comprising of Professional web, windows, mobile and cloud developers, technical managers, and architects.

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