SQL Server - How to PIVOT multi value of same key - sql

Question

How to PIVOT a column which have multi values with same Key.
For instance, we have table
ID FieldName FieldValue
1 Name Jack
1 Country Auz
1 PostCode 1234
1 Name Jhon
2 Name Leo
2 Country USA
2 PostCode 2345
I want to get the result table after pivot:
ID Name Country PostCode
1 Jack Auz 1234
1 Jhon Auz 1234
2 Leo USA 2345
I have used code with pivot function:
SELECT *
FROM (
SELECT
ID, FieldName, FieldValue
FROM Table
) AS p
PIVOT
(
MAX(FieldValue)
FOR FieldName IN ([Name], [Country], [PostCode])
) AS pvt
From the above code, The result table will only get one record for ID '1', I think this may due to the function of 'MAX' used. Is there any way to show two records by using any other function to solve it?

Answer 1

You have an unusual situation in your data because ID 1 has 2 names associated with it, and you want both to share the other attributes such as postcode etc. For this you can use an apply operator to return 1 or more names for each ID, and then group by the combination of id and name.
SELECT
id
, Name
, MAX(CASE WHEN fieldname = 'Country' THEN fieldvalue END) AS Country
, MAX(CASE WHEN fieldname = 'Postcode' THEN fieldvalue END) AS Postcode
FROM (
SELECT
t.*, ca.Name
FROM mytable AS t
CROSS APPLY (
SELECT
FieldValue AS Name
FROM mytable AS t2
WHERE t.id = t2.id
AND t2.FieldName = 'Name'
) AS ca
WHERE FieldName IN ('Country','PostCode')
) t
GROUP BY
id
, name
;
also see: https://rextester.com/GKOK78960
result:
+----+----+------+---------+----------+
| | id | Name | Country | Postcode |
+----+----+------+---------+----------+
| 1 | 1 | Jack | Auz | 1234 |
| 2 | 1 | Jhon | Auz | 1234 |
| 3 | 2 | Leo | USA | 2345 |
+----+----+------+---------+----------+
note that using cross apply is a bit like an inner join; if there is no name associated to an id, that id will not be returned by the query above. If there is a need for an id without name use outer apply instead (as this is similar to left join).
As an alternative, you could use pivot like so:
SELECT id, name, [Country], [PostCode]
FROM (
SELECT
t.*, ca.Name
FROM mytable AS t
CROSS APPLY (
SELECT
FieldValue AS Name
FROM mytable AS t2
WHERE t.id = t2.id
AND t2.FieldName = 'Name'
) AS ca
WHERE FieldName IN ('Country','PostCode')
) AS p
PIVOT
(
MAX(FieldValue)
FOR FieldName IN ([Country], [PostCode])
) AS pvt