💎SQL Reloaded: PIVOT Operator Example

Starting with SQL Server 2005, Microsoft introduced the PIVOT operator, which tries to implement the pivoting feature available in Excel, however it does only static pivoting, the values on which the pivoting is done must be mentioned explicitely.

 
In List Based Aggregations I gave an example of a query in which the On Hand was cumulated per Location, the same output can be obtained with the below query.

-- using PIVOT
SELECT Name
, ProductNumber
, MakeFlag
, FinishedGoodsFlag
, IsNull([Paint Storage], 0) OnHandPaintStorage
, IsNull([Frame Forming], 0) OnHandFrameForming
, IsNull([Frame Welding], 0) OnHandFrameWelding
, IsNull([Debur and Polish], 0) OnHandDeburPolish
, IsNull([Specialized Paint], 0) OnHandSpecializedPaint
, IsNull([Subassembly], 0) OnHandAssembly
, IsNull([Final Assembly], 0) OnHandFinalAssembly
, IsNull([Paint Storage], 0) + IsNull([Frame Forming], 0) + IsNull([Frame Welding], 0) + IsNull([Debur and Polish], 0) + IsNull([Specialized Paint], 0) + IsNull([Subassembly], 0) + IsNull([Final Assembly], 0) OnHand
, ListPrice
, StandardCost
, (IsNull([Paint Storage], 0) + IsNull([Frame Forming], 0) + IsNull([Frame Welding], 0) + IsNull([Debur and Polish], 0) + IsNull([Specialized Paint], 0) + IsNull([Subassembly], 0) + IsNull([Final Assembly], 0) ) * StandardCost Value
FROM
(
	SELECT PP.Name
	, PP.ProductNumber
	, PP.MakeFlag
	, PP.FinishedGoodsFlag
	, PL.Name AS Location
	, PP.ListPrice
	, PP.StandardCost
	, PPI.Quantity
	FROM Production.ProductInventory PPI
	     JOIN Production.Product PP
	       ON PPI.ProductID = PP.ProductID
	      JOIN Production.Location PL
	        ON PPI.LocationID = PL.LocationID
) AS A
PIVOT
(
	SUM(Quantity)
	FOR Location IN ([Paint Storage], [Frame Forming], [Frame Welding], [Debur and Polish], [Specialized Paint], [Subassembly], [Final Assembly])
) PVT

The query is not rocket science, but it took me some time to figure out that when I need to use multiple tables, I have to create first a subquery, and only then can apply the PIVOT operator. 

This is how I tried to write my query:

SELECT PP.Name
, PP.ProductNumber
, PP.MakeFlag
, PP.FinishedGoodsFlag
, IsNull([Paint Storage], 0) OnHandPaintStorage
, IsNull([Frame Forming], 0) OnHandFrameForming
, IsNull([Frame Welding], 0) OnHandFrameWelding
, IsNull([Debur and Polish], 0) OnHandDeburPolish
, IsNull([Specialized Paint], 0) OnHandSpecializedPaint
, IsNull([Subassembly], 0) OnHandAssembly
, IsNull([Final Assembly], 0) OnHandFinalAssembly
, IsNull([Paint Storage], 0) + IsNull([Frame Forming], 0) + IsNull([Frame Welding], 0) + IsNull([Debur and Polish], 0) + IsNull([Specialized Paint], 0) + IsNull([Subassembly], 0) + IsNull([Final Assembly], 0) OnHand
, PP.ListPrice
, PP.StandardCost
, (IsNull([Paint Storage], 0) + IsNull([Frame Forming], 0) + IsNull([Frame Welding], 0) + IsNull([Debur and Polish], 0) + IsNull([Specialized Paint], 0) + IsNull([Subassembly], 0) + IsNull([Final Assembly], 0) ) * StandardCost Value
FROM Production.ProductInventory PPI
JOIN Production.Product PP
ON PPI.ProductID = PP.ProductID
JOIN Production.Location PL
ON PPI.LocationID = PL.LocationID
PIVOT
(
SUM(Quantity)
FOR PL.Name IN ([Paint Storage], [Frame Forming], [Frame Welding], [Debur and Polish], [Specialized Paint], [Subassembly], [Final Assembly])
) PVT

The query generated the following errors:

Msg 8156, Level 16, State 1, Line 1

The column 'ProductID' was specified multiple times for 'PVT'.

Msg 4104, Level 16, State 1, Line 1

The multi-part identifier "PP.Name" could not be bound.

Msg 4104, Level 16, State 1, Line 1

The multi-part identifier "PP.ProductNumber" could not be bound.

Msg 4104, Level 16, State 1, Line 1

The multi-part identifier "PP.MakeFlag" could not be bound.

Msg 4104, Level 16, State 1, Line 1

The multi-part identifier "PP.FinishedGoodsFlag" could not be bound.

Msg 4104, Level 16, State 1, Line 1

The multi-part identifier "PP.ListPrice" could not be bound.

Msg 4104, Level 16, State 1, Line 1

The multi-part identifier "PP.StandardCost" could not be bound.

Notes:
1. Probably, it's better to create a view for subquery and use the view instead. I am doing that most of the times, sometimes I prefer to write table-valued functions; more on this in another post.
2. As it seems can be used only one aggregation function with PIVOT, that's pretty bad because even if you start doing your query using a PIVOT and then the requirements change (e.g. is needed to output how many records are for each Location, a more appropriate example is the ones of Purchase Orders, in which could be aggregations applied on Ordered, Receipt and Open Quantity) then you'll have to change the whole query. I'm expecting more from next implementations of PIVOT operator, I hope Microsoft will have that on their list.
3. The benefit of PIVOT operator is supposed to be that it allows writing shorter code, not necessarily. Of course, it allows to eliminate the redundant code - the multiple CASE WHEN statements, however this works when there is only one column (Location in our example) used to do the split, what if there is additional logic which must be included in CASEs?

Happy coding!

💎SQL Reloaded: List Based Aggregations (On Hand example)

    I found some time ago a query like the one below (I wrote this kind of queries myself too):
SELECT PP.Name
, PP.ProductNumber
, PP.MakeFlag
, PP.FinishedGoodsFlag
, IsNull(PI1.Quantity, 0) OnHandPaintStorage
, IsNull(PI2.Quantity, 0) OnHandFrameForming
, IsNull(PI3.Quantity, 0) OnHandFrameWelding
, IsNull(PI1.Quantity, 0)+IsNull(PI2.Quantity, 0)+IsNull(PI3.Quantity, 0) OnHand
, PP.ListPrice
, PP.StandardCost
, (IsNull(PI1.Quantity, 0)+IsNull(PI2.Quantity, 0)+IsNull(PI3.Quantity, 0))*PP.StandardCost Value
FROM Production.Product PP
LEFT JOIN
(-- On Hand Paint Storage
SELECT SUM (Quantity) Quantity
, PPI.ProductID
FROM Production.ProductInventory PPI
JOIN Production.Location PL
ON PPI.LocationID = PL.LocationID
WHERE PL.Name = 'Paint Storage' GROUP BY PPI.ProductID
) PI1
ON PP.ProductID = PI1.ProductID
LEFT JOIN
(--On Hand Frame Forming
SELECT SUM (Quantity) Quantity
, PPI.ProductID
FROM Production.ProductInventory PPI
JOIN Production.Location PL
ON PPI.LocationID = PL.LocationID
WHERE PL.Name = 'Frame Forming'
GROUP BY PPI.ProductID
) PI2
ON PP.ProductID = PI2.ProductID
LEFT JOIN
(--On Hand Frame Welding
SELECT SUM (Quantity) Quantity
, PPI.ProductID
FROM Production.ProductInventory PPI
JOIN Production.Location PL
ON PPI.LocationID = PL.LocationID
WHERE PL.Name = 'Frame Welding'
GROUP BY PPI.ProductID
) PI3
ON PP.ProductID = PI3.ProductID
WHERE IsNull(PI1.Quantity, 0)+IsNull(PI2.Quantity, 0)+IsNull(PI3.Quantity, 0) <> 0
ORDER BY PP.Name

    I exemplified the above query by using tables from AdventureWorks database, and it's based on Product, ProductInventoy and Location table.
The query returns the OnHand from special Locations (here I exemplified with only 3 locations, but could be more), the query is not difficult even if it involves 3 tables, however many people write this kind of lengthy queries. A much simpler solution is to use directly aggregations as in the below query. Such method is flexible enough to allow to add another Locations to the query in no time, and performs better!
SELECT PP.Name
, PP.ProductNumber
, PP.MakeFlag
, PP.FinishedGoodsFlag
, SUM(CASE WHEN PL.Name = 'Paint Storage' THEN PPI.Quantity ELSE 0 END) OnHandPaintStorage
, SUM(CASE WHEN PL.Name = 'Frame Forming' THEN PPI.Quantity ELSE 0 END) OnHandFrameForming
, SUM(CASE WHEN PL.Name = 'Frame Welding' THEN PPI.Quantity ELSE 0 END) OnHandFrameWelding
, SUM(CASE WHEN PL.Name = 'Debur and Polish' THEN PPI.Quantity ELSE 0 END) OnHandDeburPolish
, SUM(CASE WHEN PL.Name = 'Specialized Paint' THEN PPI.Quantity ELSE 0 END) OnHandSpecializedPaint
, SUM(CASE WHEN PL.Name = 'Subassembly' THEN PPI.Quantity ELSE 0 END) OnHandSubassembly
, SUM(CASE WHEN PL.Name = 'Final Assembly' THEN PPI.Quantity ELSE 0 END) OnHandFinalAssembly
, SUM(PPI.Quantity) OnHand
, PP.ListPrice
, PP.StandardCost
, SUM(PPI.Quantity)*PP.StandardCost Value
FROM Production.ProductInventory PPI
JOIN Production.Product PP
ON PPI.ProductID = PP.ProductID
JOIN Production.Location PL
ON PPI.LocationID = PL.LocationID
WHERE PL.Name IN ('Paint Storage', 'Frame Forming', 'Frame Welding', 'Debur and Polish', 'Specialized Paint', 'Subassembly', 'Final Assembly')
GROUP BY PP.Name
, PP.ProductNumber
, PP.MakeFlag
, PP.FinishedGoodsFlag
, PP.ListPrice
, PP.StandardCost
HAVING SUM(PPI.Quantity)<>0
ORDER BY PP.Name

Note:
1. Probably you'll wonder why I put the constraint SUM(PPI.Quantity)<>0?! The explanation is simple, I met cases in which ERP systems were allowing negative values for On Hand, pretty cool, isn't it?
2. AdventureWorks database can be downloaded from Microsoft site.
3. I met many other cases in which this type of quries are very handy, in here I tried to exemplify the method in the easiest possible way, with minimum of effort :D.

💎SQL Reloaded: The Stuff function

No matter how much experience we have in a programming language or a technology, there is always something new to learn. There are a few hardly used functions in SQL Server 2000, but they could be really useful in certain situations. One of such functions is Stuff, I discovered its use long time after I started to play with SQL. 

  Stuff ( character_expression , start , length , character_expression )

--inserting a string inside another without doing a replacement
SELECT Stuff('This is just a test', 3, 0, 'x')  -- Output: Thxis is just a test 

--inserting a string inside another without doing a replacement 
SELECT Stuff('This is just a test', 3, 5, 'at was') --Output: That was just a test  

 So, it could be useful when we check whether a character is on a certain position, and replace it with another character. Normally we would have to write something like: 

DECLARE @string varchar(50) 
SET @string = 'DE1988299X8829' 
SELECT 
    CASE WHEN Substring(@string, 10,1) = 'X' THEN Stuff(@string, 10, 1, 'Y') 
   ELSE @string 
END 

Output: DE1988299Y8829     

Another function I haven't saw too often in SQL logic is Replicate, yeah, it does exactly what it's name suggests - it takes a string and replicates it's content multiple times. 

 Replicate ( character_expression , integer_expression ) 

 SELECT Replicate ('0', 10) --Output: 0000000000 
 SELECT Replicate ('tone', 3) --Output: tonetonetone     

The function could be useful when we need to put a number of characters in front of a value. For example a table contains integer values, but in a report we need them with leading zeroes (e.g. 00056 instead of 56). I tried to implement such functionality as a function, in a previous posting with the help of Space function; using Space and Replace functions can be obtained the same result as using Replicate: 

  SELECT Replace(Space(3), ' ', 'tone') --Output: tonetonetone

Notes:
The code has been tested successfully also on a SQL database in Microsoft Fabric.

Happy coding!

💎SQL Reloaded: Useful Functions in Data Conversion

    When working with data, even if it's about reporting, data conversion or data analysis, there are a few useful functions which makes life easier. They deal with three types of basic variables and their variations: strings (e.g. char, varchar), numeric (e.g. int, decimal) and date (e.g. smalldatetime, datetime).  

1. Case Function

CASE input_expression 
        WHEN when_expression 
        THEN result_expression [ ...n ] 
       [ELSE else_result_expression] 
END   

        

Judging from experience, CASE is the most used function in data conversions, when the output value is based on on one or multiple constraints over the already existing values. 

  

CASE WHEN column1 = 'yes' OR column2 = 'other' THEN 'yes/other' END    

 Just be careful, when the ELSE is not provided, a null will be returned! 

Another important thing, the values returned must have the same base type, dates, strings or numeric values can't be mixed without conversion! 

--example 1 
CASE 
    WHEN DateDiff(d, DateValue, GetDate())>0 THEN 'past' WHEN DateDiff(d, DateValue, GetDate())=0 THEN 'today' 
    ELSE 'future' 
END 

--example 2 
CASE 
     WHEN column1 BETWEEN 1 AND 100 THEN '1st range' 
     WHEN column1 BETWEEN 101 AND 1000 THEN '2nd range' 
     ELSE '3rd range' 
END 

--example 3 
CASE 
    WHEN column1 IN ('A', 'B', 'C') THEN '1st set' 
    WHEN column1 IN ('C', 'D', 'E') THEN '2nd set' 
    ELSE '3rd set' 
END      

 There is a saying for DBAs and not only, "Know your data!". As each statement is checked until comparison operation evaluated True, it is better to arrange the WHEN expression in the descending order of highest occurrence. 

 2. IsNull Function

IsNull(expression)   

  

 It's always a good idea to check for NULL values, they could occur anytime when a default value is not provided for a value. One of the cases I often found was when joining two tables when one of the values from JOIN was NULL. 

-- example for string values 
SELECT * 
FROM table1 A 
         LEFT JOIN table2 B 
             ON A.column1 = B.column1 
           AND IsNull(A.column2, ' ') = IsNull(B.column2, ' ') 
WHERE B.column1 IS NULL  

-- example for numeric values 
SELECT * 
FROM table1 A 
      LEFT JOIN table2 B 
          ON A.column1 = B.column1  
        AND IsNull(A.column2, 0) = IsNull(B.column2, 0) 
WHERE B.column1 IS NULL 

The ' ' and 0 values should be used when they aren't found in the list of possible values or there is no impact on the result. Another used value for IsNull function is 'N/A', to point out the missing value. 

 3. Coalesce Function

COALESCE ( expression [ ,...n ] )  

       

There are cases when is needed to take the first not null value from a list of columns, could be dates or any type of other value. Instead of writting something like IsNull(Date1, IsNull(Date2, IsNull(Date3, GetDate()) it's much easier to write COALESCE(Date1, Date2, Date3, GetDate()) 

-- example coalesce 
SELECT * 
FROM table1 
WHERE COALESCE(Column1, Column2, Column3) IS NOT NULL 

-- example IsNull alternative 
SELECT * 
FROM table1 
WHERE Column1 IS NOT NULL 
        OR Column2 IS NOT NULL 
        OR Column3 IS NOT NULL 

 4. NullIf Function

  

NullIf ( expression , expression )    

NullIf function is handy especially when is not needed a certain value in output, for example 0 or the .  

-- example numeric values 
SELECT column1
, NullIf(column2, 0) column2
FROM table_name     

-- example string or date values 
SELECT column1
, NullIf(column2, '') column2
FROM table_name     

When multiple values are not needed, it's easier maybe to write 

-- example multiple checks 
 SELECT column1 
, CASE 
     WHEN column2 IN ('A', 'B', 'V') THEN NULL 
     ELSE column1 END 
FROM table_name 

-- alternative 
SELECT column1, NullIf(NullIf(NullIf(column2, 'A'), 'B'), 'V') 
FROM table_name

 5. Convert Function

CONVERT ( data_type [ ( length ) ] , expression [ , style ] )       

 I used to use CAST instead CONVERT, however CONVERT is more powerful, especially when it comes to dates. SQL Server comes with a few dates formats obtain by providing a value for style parameter: 

SELECT CONVERT(varchar(10), GetDate(),101) -- US format: mm/dd/yyyy
SELECT CONVERT(varchar(10), GetDate(),102) -- ANSI format: yyyy.mm.dd
SELECT CONVERT(varchar(10), GetDate(),103) -- British/French dd/mm/yyyy
SELECT CONVERT(varchar(10), GetDate(),104) -- German format: dd.mm.yyyy
SELECT CONVERT(varchar(12), GetDate(),105) -- Italian format: dd-mm-yyyy
SELECT CONVERT(varchar(12), GetDate(),106) -- dd mon yyyy
SELECT Upper(CONVERT(varchar(12), GetDate(),106))   -- upper case of: dd mon yyyy
SELECT CONVERT(varchar(8), GetDate(),112) -- ISO format (preferred): yyyymmdd
SELECT CONVERT(varchar(10), GetDate(), 23) -- yyyy-mm-dd
SELECT CONVERT(varchar(23), GetDate(),126) -- yyyy-mm-ddThh:mi:ss.mmm

The conversion of a date to a string is mainly required by the need to have the date in a special format or not allow Excel to format the date to its default. 

 6. IsNumeric Function

IsNumeric ( expression )     

This function shouldn't miss when casting string values to numeric values and doing operations with them. 

SELECT CAST(column1 as decimal(12,2)) + 101 
FROM table_name 
WHERE IsNumeric(column1)=1     

Please note that when multiple constraints are used, the IsNumeric function should appear first after the WHERE clause, a query like the next one might raise an error if one of the column1 values is not numeric. 

-- example 
SELECT CAST(column1 as decimal(12,2)) + 101 
FROM table_name 
WHERE column2 = 'value' 
AND IsNumeric(column1)=1

-- alternative writing (recommended)
SELECT CAST(column1 as decimal(12,2)) + 101 
FROM table_name WHERE IsNumeric(column1)=1 
   AND column2 = 'value' 

 7. IsDate Function

IsDate( expression )          

 It works the same way as IsNumeric, but on date data types. Thus if the provided values is a date, it will return 1, otherwise 0. 

  SELECT IsDate(GetDate()) 
  SELECT IsDate('11/31/2007') --november has only 30 days 
  SELECT CASE IsDate('11/31/2007') WHEN 1 THEN 'Yes' ELSE 'No' END 

Note:     
For more information on the function is always a good idea to consult Microsoft Technical documentation.

Happy coding!

💎SQL Reloaded: XML on SQL Server 2005

This is a homework I did for my masters degree (still studying). Unfortunately, studying after my normal work hours doesn't give me much time to post. Therefore, this post has only short comments.  Hopefully, it will be helpful for somebody!

-- creating a table for demonstration purposes ID - identity field Books - XML document where the tables are stored  
CREATE TABLE XMLBooks( 
  ID int IDENTITY(1,1) PRIMARY KEY 
, Books XML) 

-- dropping the table
--DROP TABLE XMLBooks 

-- inserting a record - an XML document containing one book
INSERT INTO XMLBooks 
VALUES ('<books> 
<book id="1" language="EN"> <title>Inside SQL Server 2005 Tools</title> <authors> <author>Michael Raheem</author> <author>Dima Sonkin</author> <author>Thierry D''Hers</author> <author>Kami LeMonds</author> </authors> <year>2006</year> <publisher>Addison Wesley</publisher> <price></price> <pages>816</pages> <isbn10>0-321-39796-7</isbn10> <isbn13>978-0-321-39796-6</isbn13> </book> 
</books>') 

-- inserting a records - an XML document containing three books
INSERT INTO XMLBooks 
VALUES ('<books> 

<book id="2" language="EN"> <title>Core C# and .NET</title> <authors> <author>Stephen C. Perry</author> </authors> <year>2005</year> <publisher>Prentice Hall</publisher> <price></price> <pages>1008</pages> <isbn10>0-13-147227-5</isbn10> <isbn13></isbn13> </book> 
<book id="3" language="EN"> <title> Microsoft SQL Server 2005</title> <authors> <author>Andrew J. Brust</author> <author>Stephen Forte</author> </authors> <year>2006</year> <publisher>Microsoft Press</publisher> <price></price> <pages>600</pages> <isbn10>0-7356-1923-9</isbn10> <isbn13>978-0-7356-1923-4</isbn13> </book> 
<book id="4" language="EN"> <title>MCAD/MCSD: Visual Basic .NET XML Web Services and Server Components Study Guide</title> <authors> <author>Pamela Fanstill</author> <author>Brian Reisman </author> <author>Mitch Ruebush</author> </authors> <year>2003</year> <publisher>Sybex</publisher> <price></price> <pages>598</pages> <isbn10>0-7821-4193-5</isbn10> <isbn13></isbn13> </book> 
</books>') 


-- a classical SELECT */ 
SELECT * FROM XMLBooks 

-- a first XML falvoured query
SELECT Books.query('/.') FROM XMLBooks 


-- selecting an element's content*/ 
SELECT Books.query('//book[@id=1]/title/text()')
FROM XMLBooks 


-- selecting an element's content
SELECT Books.value('data(//book[@id=1]/title/)','varchar(250)') 
FROM XMLBooks 

The last statement leads to the following error message:

Msg 2256, Level 16, State 1, Line 2 XQuery [XMLBooks.Books.value()]: Syntax error near ')', expected a "node test". 

-- selecting an element's content 
SELECT Books.value('data((//book[@id=1]/title)[1])','varchar(250)') 
FROM XMLBooks 

-- selecting only the occurence
SELECT Books.value('data((//book[@id=1]/title)[1])','varchar(250)') 
FROM XMLBooks 
WHERE Books.exist('//book[@id=1]')=1 

-- updating a node by inserting a new child after an existing one 
UPDATE XMLBooks
SET Books.modify('insert Jack Daniels after (//book[@id=1]//author)[1]') 

-- updating a node */ 
UPDATE XMLBooks
SET Books.modify(' insert Jack Daniels before (//book[@id=1]//author)[1]') 

-- deleting a child  
UPDATE XMLBooks 
SET Books.modify(' delete //book[@id=1]//author[1]') 

-- modifying an attribute 
UPDATE XMLBooks 
SET Books.modify(' replace value of (//book/@id)[1] with "100"') 

-- deleting a record 
DELETE FROM XMLBooks 
WHERE Books.exist('//book[@id=1]')=1 

SELECT Book.Athors.query('/.') AS AuthorsList 
FROM XMLBooks.nodes('/books/book/authors') Book(Authors)

Happy coding!

💎SQL Reloaded: Null-ifying the World

Do you remember the table used in previous post? In the respective case we provided all the values, what happens when a value is missing? How do we deal with such cases? For such cases we have the value NULL. Let's try to insert a NULL in one of the columns:

 

CREATE TABLE Table1(
ID int
, [Year] int
, Product varchar(30)
, Price decimal(13,2)
, Quantity decimal(13,3))

 

Then we inserted in the table test data, let's try to insert also a NULL for one of the values:

 

-- inserting the test data 
INSERT Table1(ID, [Year], Product, Price, Quantity)
VALUES (1, 2002, NULL, 199.23, 100)

--checking table's content
SELECT *
FROM Table1

We can check for NULL values using the IS NULL clasuse:

 

-- checking for NULLs
SELECT *
FROM Table1
WHERE Product IS NULL

If you don't like NULL values, you can replace them with other values, with the help of IsNull function. 

-- handling NULL values with a text 
SELECT ID, [Year], IsNull (Product, 'missing value'), Price, Quantity
FROM Table1

-- handling NULL values with a text (different result)
SELECT ID, [Year], IsNull(Product, 'The Prouct value is missing! Please correct it!') Product, Price, Quantity
FROM Table1

   As you can see, because the maximum length of Product column is 30, the text is trimmed after 30 characters. In order to solve this issue, we can reduce the error message to maximum 30 characters or convert the Product type from varchar(30) to varchar(50), enough to hold the whole string:

SELECT ID, [Year], IsNull(Cast(Product as varchar(50)), 'The Prouct value is missing! Please correct it!') Product, Price, Quantity
FROM Table1

-- inserting more NULL values.
INSERT Table1(ID, [Year], Product, Price, Quantity)
VALUES (1, 2002, 'Product 6', NULL, 100)
INSERT Table1(ID, [Year], Product, Price, Quantity)
VALUES (1, 2002, 'Product 7', 45.08, NULL)
INSERT Table1(ID, [Year], Product, Price, Quantity)
VALUES (1, 2002, 'Product 8', NULL, NULL)
INSERT Table1(ID, [Year], Product, Price, Quantity)
VALUES (1, NULL, 'Product 9', NULL, NULL)

      

 When we need to test for NULL values in multiple columns we could write something like this:

 

-- individual checks 
SELECT *
FROM Table1
WHERE Price IS NULL
OR Quantity IS NULL

-- simpler alternative 
SELECT *
FROM Table1
WHERE IsNull(Price1, Price2) IS NULL

These checks are useful when you need to check for two values which shouldn't be simultaneously NULL. For more columns with possible NULL values, when the values have the same type, we can rewrite the statements as follows:

 

-- checking for multiple values
SELECT *
FROM Table1
WHERE COALESCE(Price1, Price2, Price3) IS NULL

-- replacing NULL values 
SELECT ID
, [Year]
, IsNull(Product, 'The Prouct value is missing!') Product
, IsNull(Price, 0)
, IsNull(Quantity, 0)
FROM Table1

When inserting NULL values in a column with a NOT NULL constraint, the following error message will be shown:

"Msg 515, Level 16, State 2, Line 1 Cannot insert the value NULL into column 'Product', table 'Learning.dbo.Table1'; column does not allow nulls. INSERT fails."

--dropping the table
DROP TABLE Table1

-- creating the table anew
CREATE TABLE Table1(
ID NOT NULL
, [Year] int NOT NULL
, Product varchar(30) NOT NULL
, Price decimal(13,2) NOT NULL
, Quantity decimal(13,3) NOT NULL)

-- inserting NULL values
INSERT Table1(ID, [Year], Product, Price, Quantity)
VALUES (1, 2002, NULL, 199.23, 100)

 

 Another way is to use defaults, thus if a value was not provided, it will be replaced with the DEFAULT values:

 

-- creating the table anew
CREATE TABLE Table1(
  ID int NOT NULL
, [Year] int NOT NULL
, Product varchar(30) DEFAULT 'Unknown' 
, Price decimal(13,2) NOT NULL
, Quantity decimal(13,3) NOT NULL)

-- Inserting some values
INSERT Table1(ID, [Year], Price, Quantity)
VALUES (1, 2002, 199.23, 100)
INSERT Table1(ID, [Year], Product, Price, Quantity)
VALUES (1, 2002, NULL, 199.23, 100)

--testing the output
SELECT *
FROM Table1

Notes:
The code has been tested successfully also on a SQL database in Microsoft Fabric.

Happy coding!