SQL Pivot Command - sql

Question

I am looking for some help on designing a simple pivot so that I can link it into other parts of my queries.
My data is like this
Items Table
Below is my table if I run Select * from items
ITEM Weight
12345 10
12345 11
654321 50
654321 20
654321 100
There are hundreds of Items in this table but each item code will only ever have
maximum of 3 weight records each.
I want the desired output
ITEM Weight_1 Weight_2 Weight_3
12345 10 11 null
654321 50 20 100
Would appreciate any suggestions,
I have played around with pivots but each subsequent item puts the weights into weight 4,5,6,7,etc
instead of starting at weight1 for each item.
Thanks
Update
Below is what I have used so far,
SELECT r.*
FROM (SELECT 'weight' + CAST(Row_number() OVER (ORDER BY regtime ASC)AS
VARCHAR(10))
line,
id,
weight
FROM items it) AS o PIVOT(MIN([weight]) FOR line IN (weight1, weight2,
weight3)) AS r

Answer 1

You were almost there! You were only missing the PARTITION BY clause in OVER:
SELECT r.*
FROM (SELECT 'weight' + CAST(Row_number() OVER (PARTITION BY id ORDER BY
regtime ASC)
AS
VARCHAR(10)) line,
id,
weight
FROM items it) AS o PIVOT(MIN([weight]) FOR line IN (weight1, weight2,
weight3)) AS r
When you PARTITION BY by ID, the row numbers are reset for each different ID.
Update
You do not need dynamic pivot, since you will always have 3 weights. But, if you ever need dynamic number of columns, take a look at some of the examples here:
SQL Server PIVOT perhaps?
Pivot data in T-SQL
How do I build a summary by joining to a single table with SQL Server?

Answer 2

You will need a value to form the columns which I do with row_number. The outcome is what you want. The only negative that I have against PIVOT is that you need to know how many columns in advance. I use a similar method, but build up the select as dynamic SQL and can then insert my columns.
EDIT: updated to show columns as weight1, weight2, etc.
create table #temp (Item int, Weight int)
insert into #temp (Item, Weight)
Values (12345, 10),
(12345, 11),
(654321, 50),
(654321, 20),
(654321, 200)
SELECT *
FROM (SELECT Item,
Weight,
'weight' + cast(Row_number()
OVER (partition by Item order by item) as varchar(10)) as seq
FROM #temp) as Src
PIVOT ( MAX(Weight) FOR Seq IN ([Weight1], [Weight2], [Weight3]) ) as PVT

Answer 3

MySQL
Whenever you need a pivot, use group_concat it will output a CSV list of the values you need.
Once you get used to working with it, it's a great tool.
SELECT item, GROUP_CONCAT(weight) as weights FROM table1
GROUP BY item
See: http://dev.mysql.com/doc/refman/5.0/en/group-by-functions.html#function_group-concat
TSQL aka SQL-server
Many many questions on this because T-SQL supports a pivot keyword.
See:
Transact SQL Query-Pivot-SQL
Pivot data in T-SQL