How to Concatenate Emails by Report ID Using SQL Server's GROUP BY Clause?

SQL Server: Concatenating Emails within Report ID Groups Using GROUP BY

In SQL Server, efficiently grouping data and combining related values into single strings is a common task. The GROUP BY clause groups rows based on specified columns, enabling aggregate function use for data manipulation and calculations.

Combining Emails by Report ID

Imagine a table structured like this:

<code>ID    ReportId     Email
1     1            [email protected]
2     2            [email protected]
3     1            [email protected]
4     3            [email protected]
5     3            [email protected]</code>

The goal is to group rows by ReportId and concatenate corresponding emails into comma-separated strings. The desired output:

<code>ReportId     Email
1            [email protected], [email protected]
2            [email protected]
3            [email protected], [email protected]</code>

Leveraging the STUFF() Function

This is effectively achieved using the STUFF() function within a subquery:

SELECT ReportId, Email = 
    STUFF((SELECT ', ' + Email
           FROM your_table b 
           WHERE b.ReportId = a.ReportId 
          FOR XML PATH('')), 1, 2, '')
FROM your_table a
GROUP BY ReportId

Detailed Explanation:

• The inner subquery selects all emails for each ReportId, prepending each email with a comma and space.
• FOR XML PATH('') transforms the subquery results into a single XML string.
• STUFF() removes the leading comma and space from the XML string, resulting in the desired comma-separated email list.

Further Considerations:

• Other aggregate functions (e.g., SUM(), AVG()) can be used with GROUP BY for various calculations on grouped data.
• STUFF() is a highly versatile function for diverse string manipulation operations.

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