AdventureWorks Database: Select data from first column that has a nonnull value

SQL Query - AdventureWorks: Exercise-130 with Solution

130. From the following table write a query in SQL to select the data from the first column that has a nonnull value. Retrun Name, Class, Color, ProductNumber, and FirstNotNull.

productid|name                            |productnumber|makeflag|finishedgoodsflag|color       |safetystocklevel|reorderpoint|standardcost|listprice|size|sizeunitmeasurecode|weightunitmeasurecode|weight |daystomanufacture|productline|class|style|productsubcategoryid|productmodelid|sellstartdate          |sellenddate            |discontinueddate|rowguid                             |modifieddate           |
---------+--------------------------------+-------------+--------+-----------------+------------+----------------+------------+------------+---------+----+-------------------+---------------------+-------+-----------------+-----------+-----+-----+--------------------+--------------+-----------------------+-----------------------+----------------+------------------------------------+-----------------------+
        1|Adjustable Race                 |AR-5381      |false   |false            |            |            1000|         750|           0|        0|    |                   |                     |       |                0|           |     |     |                    |              |2008-04-30 00:00:00.000|                       |                |694215b7-08f7-4c0d-acb1-d734ba44c0c8|2014-02-08 10:01:36.827|
        2|Bearing Ball                    |BA-8327      |false   |false            |            |            1000|         750|           0|        0|    |                   |                     |       |                0|           |     |     |                    |              |2008-04-30 00:00:00.000|                       |                |58ae3c20-4f3a-4749-a7d4-d568806cc537|2014-02-08 10:01:36.827|
        3|BB Ball Bearing                 |BE-2349      |true    |false            |            |             800|         600|           0|        0|    |                   |                     |       |                1|           |     |     |                    |              |2008-04-30 00:00:00.000|                       |                |9c21aed2-5bfa-4f18-bcb8-f11638dc2e4e|2014-02-08 10:01:36.827|
        4|Headset Ball Bearings           |BE-2908      |false   |false            |            |             800|         600|           0|        0|    |                   |                     |       |                0|           |     |     |                    |              |2008-04-30 00:00:00.000|                       |                |ecfed6cb-51ff-49b5-b06c-7d8ac834db8b|2014-02-08 10:01:36.827|
      316|Blade                           |BL-2036      |true    |false            |            |             800|         600|           0|        0|    |                   |                     |       |                1|           |     |     |                    |              |2008-04-30 00:00:00.000|                       |                |e73e9750-603b-4131-89f5-3dd15ed5ff80|2014-02-08 10:01:36.827|
      317|LL Crankarm                     |CA-5965      |false   |false            |Black       |             500|         375|           0|        0|    |                   |                     |       |                0|           |L    |     |                    |              |2008-04-30 00:00:00.000|                       |                |3c9d10b7-a6b2-4774-9963-c19dcee72fea|2014-02-08 10:01:36.827|
      318|ML Crankarm                     |CA-6738      |false   |false            |Black       |             500|         375|           0|        0|    |                   |                     |       |                0|           |M    |     |                    |              |2008-04-30 00:00:00.000|                       |                |eabb9a92-fa07-4eab-8955-f0517b4a4ca7|2014-02-08 10:01:36.827|
	  -- more --

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Sample Solution:

-- Selecting specific columns from the Product table and using COALESCE function to find the first non-null value among Class, Color, and ProductNumber
SELECT 
    -- Selecting the Name column
    Name, 
    -- Selecting the Class column
    Class, 
    -- Selecting the Color column
    Color, 
    -- Selecting the ProductNumber column
    ProductNumber,  
    -- Applying the COALESCE function to find the first non-null value among Class, Color, and ProductNumber
    COALESCE(Class, Color, ProductNumber) AS FirstNotNull  
-- Selecting data from the Product table
FROM 
    Production.Product;

Explanation:

• This SQL code selects specific columns from the Product table and uses the COALESCE function to find the first non-null value among Class, Color, and ProductNumber for each row.
• The COALESCE function returns the first non-null value from the list of its arguments.
• If Class is not null, it is returned.
• If Class is null but Color is not null, Color is returned.
• If both Class and Color are null but ProductNumber is not null, ProductNumber is returned.
• The result set includes columns for Name, Class, Color, ProductNumber, and the first non-null value among Class, Color, and ProductNumber, labeled as FirstNotNull.
• This SQL query can be useful for scenarios where you need to select a fallback value among multiple columns based on their nullability.

Sample Output:

name                            |class|color       |productnumber|firstnotnull|
--------------------------------+-----+------------+-------------+------------+
Adjustable Race                 |     |            |AR-5381      |AR-5381     |
Bearing Ball                    |     |            |BA-8327      |BA-8327     |
BB Ball Bearing                 |     |            |BE-2349      |BE-2349     |
Headset Ball Bearings           |     |            |BE-2908      |BE-2908     |
Blade                           |     |            |BL-2036      |BL-2036     |
LL Crankarm                     |L    |Black       |CA-5965      |L           |
ML Crankarm                     |M    |Black       |CA-6738      |M           |
HL Crankarm                     |     |Black       |CA-7457      |Black       |
Chainring Bolts                 |     |Silver      |CB-2903      |Silver      |
Chainring Nut                   |     |Silver      |CN-6137      |Silver      |
Chainring                       |     |Black       |CR-7833      |Black       |
Crown Race                      |     |            |CR-9981      |CR-9981     |
Chain Stays                     |     |            |CS-2812      |CS-2812     |
Decal 1                         |     |            |DC-8732      |DC-8732     |
...

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