2 Rows to 1 Row - Nested Query - sql

Question

I have a response column that stores 2 different values for a same product based on question 1 and question 2. That creates 2 rows for each product but I want only one row for each product.
Example:
select Product, XNumber from MyTable where QuestionID IN ('Q1','Q2')
result shows:
Product XNumber
Bat abc
Bat abc12
I want it to display like below:
Product Xnumber1 Xnumber2
Bat abc abc12
Please help.
Thanks.

Answer 1

If you always have two different values you can try this:
SELECT a.Product, a.XNumber as XNumber1, b.XNumber as XNumber2
FROM MyTable a
INNER JOIN MyTable b
ON a.Product = b.Product
WHERE a.QuestionId = 'Q1'
AND b.QuestionId = 'Q2'
I assume that XNumber1 is the result for Q1 and Xnumber2 is the result for Q2.

Answer 2

This will work best if you don't have answers for both Q1 and Q2 for all ids
SELECT a.Product, b.XNumber as XNumber1, c.XNumber as XNumber2
FROM (SELECT DISTINCT Product FROM MyTable) a
LEFT JOIN MyTable b ON a.Product = b.Product AND b.QuestionID = 'Q1'
LEFT JOIN MyTable c ON a.Product = c.Product AND c.QuestionID = 'Q2'

Answer 3

This is one way to achieve your expected results. However, it relies on knowing that only xNumber abc and abc12 are the values. If this is not the case, then a dynamic pivot would be likely needed.
SELECT product, max(case when XNumber = 'abc' then xNumber end) as XNumber1,
max(Case when xNumber = 'abc12' then xNumber end) as xNumber2
FROM MyTable
GROUP BY Product
The problem is that SQL needs to know how many columns will be in the result at the time it compiles the SQL. Since the number of columns could be dependent on the data itself (2 rows vs 5 rows) it can't complete the request. Using Dynamic SQL you can find out the number of rows, then pass those values in as the column names which is why the dynamic SQL works.

Answer 4

This will get you two columns, the first will be the product, and the 2nd will be a comma delimited list of xNumbers.
SELECT DISTINCT T.Product,
xNumbers = Stuff((SELECT DISTINCT ', ' + T1.XNumber
FROM MyTable T1
WHERE t.Product = T1.Product
FOR XML PATH ('')),1,1,'')
FROM MyTable T
To get what you want, we need to know how many columns there will be, what to name them, and how to determine which value goes into which column

Answer 5

Been using rank() a lot in current code we have been working on at my day job. So this fun variant came to mind for your solution.
Using rank to get the 1st, 2nd, and 3rd possible item identifier then grouping them to create a simulated pivot
DECLARE #T TABLE (PRODUCT VARCHAR(50), XNumber VARCHAR(50))
INSERT INTO #T VALUES
('Bat','0-12345-98765-6'),
('Bat','0-12345-98767-2'),
('Bat','0-12345-98768-1'),
('Ball','0-12345-98771-6'),
('Ball','0-12345-98772-7'),
('Ball','0-12345-98777-9'),
('Hat','0-12345-98711-6'),
('Hat','0-12345-98712-3'),
('Tee','0-12345-98465-1')
SELECT
PRODUCT,
MAX(CASE WHEN I = 1 THEN XNumber ELSE '' END) AS Xnumber1,
MAX(CASE WHEN I = 2 THEN XNumber ELSE '' END) AS Xnumber2,
MAX(CASE WHEN I = 3 THEN XNumber ELSE '' END) AS Xnumber3
FROM
(
SELECT
PRODUCT,
XNumber,
RANK() OVER(PARTITION BY PRODUCT ORDER BY XNumber) AS I
FROM #T
) AS DATA
GROUP BY
PRODUCT