AdventureWorks Database: Show 'N/A' instead of null and names separated by commas

SQL Query - AdventureWorks: Exercise-73 with Solution

73. From the following table write a query in SQL to replace null values with 'N/A' and return the names separated by commas in a single row.

businessentityid|persontype|namestyle|title|firstname               |middlename      |lastname              |suffix|emailpromotion|additionalcontactinfo|demographics|rowguid                             |modifieddate           |
----------------+----------+---------+-----+------------------------+----------------+----------------------+------+--------------+---------------------+------------+------------------------------------+-----------------------+
               1|EM        |false    |     |Ken                     |J               |Sánchez               |      |             0|                     |[XML]       |92c4279f-1207-48a3-8448-4636514eb7e2|2009-01-07 00:00:00.000|
               2|EM        |false    |     |Terri                   |Lee             |Duffy                 |      |             1|                     |[XML]       |d8763459-8aa8-47cc-aff7-c9079af79033|2008-01-24 00:00:00.000|
               3|EM        |false    |     |Roberto                 |                |Tamburello            |      |             0|                     |[XML]       |e1a2555e-0828-434b-a33b-6f38136a37de|2007-11-04 00:00:00.000|
               4|EM        |false    |     |Rob                     |                |Walters               |      |             0|                     |[XML]       |f2d7ce06-38b3-4357-805b-f4b6b71c01ff|2007-11-28 00:00:00.000|
               5|EM        |false    |Ms.  |Gail                    |A               |Erickson              |      |             0|                     |[XML]       |f3a3f6b4-ae3b-430c-a754-9f2231ba6fef|2007-12-30 00:00:00.000|
               6|EM        |false    |Mr.  |Jossef                  |H               |Goldberg              |      |             0|                     |[XML]       |0dea28fd-effe-482a-afd3-b7e8f199d56f|2013-12-16 00:00:00.000|
               7|EM        |false    |     |Dylan                   |A               |Miller                |      |             2|                     |[XML]       |c45e8ab8-01be-4b76-b215-820c8368181a|2009-02-01 00:00:00.000|
               8|EM        |false    |     |Diane                   |L               |Margheim              |      |             0|                     |[XML]       |a948e590-4a56-45a9-bc9a-160a1cc9d990|2008-12-22 00:00:00.000|
               9|EM        |false    |     |Gigi                    |N               |Matthew               |      |             0|                     |[XML]       |5fc28c0e-6d36-4252-9846-05caa0b1f6c5|2009-01-09 00:00:00.000|
			   -- more --

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Sample Solution:

-- Concatenating non-null values of the 'firstname' column separated by a comma and space,
-- and aliasing the result as 'test'
SELECT STRING_AGG(coalesce(firstname, ' N/A'), ', ') AS test 

-- From the Person schema's Person table
FROM Person.Person;

Explanation:

• The SQL query retrieves data from the Person table within the Person schema.
• The STRING_AGG() function concatenates non-null values of the 'firstname' column separated by a comma and space.
• The coalesce() function ensures that if the 'firstname' column contains null values, they are replaced with 'N/A' before concatenation.
• The result of the concatenation is aliased as 'test'.
• Comments are provided for each code line to explain the purpose and functionality of the code.

Sample Output:

test                                                                                                                                                                                                                                                           |
---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
Ken, Terri, Roberto, Rob, Gail, Jossef, Dylan, Diane, Gigi, Michael, Ovidiu, Thierry, Janice, Michael, Sharon, David, Kevin, John, Mary, Wanida, Terry, Sariya, Mary, Jill, James, Peter, Jo, Guy, Mark, Britta, Margie, Rebecca, Annik, Suchitra, Brandon, Jos|

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