How to UPDATE pivoted table in SQL SERVER - sql

Question

I have flat table which I have to join using EAN attribute with my main table and update gid (id of my main table).
id attrib value gid
1 weight 10 NULL
1 ean 123123123112 NULL
1 color blue NULL
2 weight 5 NULL
2 ean 331231313123 NULL
I was trying to pivot ean rows into column, next join on ean both tables, and for this moment everything works great.
--update SideTable
--set gid = ab_id
select gid, ab_id
from SideTable
pivot (max (value) for attrib in ([EAN],[MPN])) as b
join MainTable as c
on c.ab_ean = b.EAN
where b.EAN !='' AND c.ab_archive = '0'
When I am selecting both id columns is okey, but when I am uncomment first lines and delete select whole table is set with first gid from my main table.
It have to set my main id into all attributes where ID where ean is matched from my main table.
I am sorry for my terrible english but I hope someone can help me, with that.

Answer 1

The reason your update does not work is that you don't have any link between your source and target for the update, although you reference sidetable in the FROM clause, this is effectively destroyed by the PIVOT function, leaving no link back to the instance of SideTable that you are updating. Since there is no link, all rows are updated with the same value, this will be the last value encountered in the FROM.
This can be demonstrated by running the following:
DECLARE #S TABLE (ID INT, Attrib VARCHAR(50), Value VARCHAR(50), gid INT);
INSERT #S
VALUES
(1, 'weight', '10', NULL), (1, 'ean', '123123123112', NULL), (1, 'color', 'blue', NULL),
(2, 'weight', '5', NULL), (2, 'ean', '331231313123', NULL);
SELECT s.*
FROM #S AS s
PIVOT (MAX(Value) FOR attrib IN ([EAN],[MPN])) AS pvt;
You clearly have a table aliased s in the FROM clause, however because you have used pivot you cannot use SELECT s*, you get the following error:
The column prefix 's' does not match with a table name or alias name used in the query.
You haven't provided sample data for your main table, but I am about 95% certain your PIVOT is not needed, I think you can get your update using just normal JOINs:
UPDATE s
SET gid = ab_id
FROM SideTable AS s
INNER JOIN SideTable AS ean
ON ean.ID = s.ID
AND ean.attrib = 'ean'
INNER JOIN MainTable AS m
ON m.ab_EAN = ean.Value
WHERE m.ab_archive = '0'
AND m.ab_EAN != '';

Answer 2

As per comment to the question, you need to use update + select statement.
A standard version looks like:
UPDATE
T
SET
T.col1 = OT.col1,
T.col2 = OT.col2
FROM
Some_Table T
INNER JOIN
Other_Table OT
ON
T.id = OT.id
WHERE
T.col3 = 'cool'
As to your needs:
update a
set a.gid = p.ab_id
from SideTable As a
Inner join (
select gid, ab_id
from SideTable
pivot (max (value) for attrib in ([EAN],[MPN])) as b
join MainTable as c
on c.ab_ean = b.EAN
where b.EAN !='' AND c.ab_archive = '0') p ON a.ean = p.EAN

Answer 3

try and break it down a bit more like this..
update SideTable
set SideTable.gid = p.ab_id
FROM
(
select gid, ab_id
from SideTable
pivot (max (value) for attrib in ([EAN],[MPN])) as b
join MainTable as c
on c.ab_ean = b.EAN
where b.EAN !='' AND c.ab_archive = '0'
) p
WHERE p.EAN = SideTable.EAN