I have a table "Item" with a number of related items, like so:
ID Rel_ID Name RelRank
--- ------ ---- -------
1 1 foo 1
2 1 bar 2
3 1 zam 3
4 2 foo2 1
I'm trying to get a query so items with the same Rel_ID would appear in the same row, like so:
Rel_ID Name1 Name2 Name3
------ ----- ----- -----
1 foo bar zam
2 foo2
I've tried selecting the table multiple times:
SELECT k.Rel_ID, k.name 'Name1', k2.name 'Name2'
FROM item k, item k2
WHERE k.Rel_ID = k2.Rel_ID
But this fails. Surely there's a transformation or query that could drastically simplify the process, and I'm just missing it because I haven't used SQL in this way before. What am I missing?
[Edit: added RelRank column, which does appear in my data]
Regardless of the database you are using, the concept of what you are trying to achieve is called "Pivot Table".
Here's an example for mysql: http://en.wikibooks.org/wiki/MySQL/Pivot_table
Some databases have builtin features for that, see the links below.
SQLServer: http://msdn.microsoft.com/de-de/library/ms177410.aspx
Oracle: http://www.dba-oracle.com/t_pivot_examples.htm
You can always create a pivot by hand. Just select all the aggregations in a result set and then select from that result set. Note, in your case, you can put all the names into one column using concat (i think that's group_concat in mysql), since you cannot know how many names are related to a a rel_id.
pseudo-select for your case (i don't know mysql):
select rel_id, group_concat(name) from item group by rel_id