How to transform vertical data into horizontal data with SQL?

Question

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          


        

Answer 1

if the names that you listed are static,my below query that i runned sucessfully in sqlfiddle will work

SELECT rel_id,
MAX (DECODE (rel_id, '1', DECODE (relrank, '1', name) , '2',DECODE (relrank, '1', name))) NAME1,
MAX (DECODE (rel_id, '1', DECODE (relrank, '2', name))) NAME2,
MAX (DECODE (rel_id, '1', DECODE (relrank, '3', name))) NAME3
FROM supportContacts
GROUP BY rel_id

heres the SQL fiddle

http://sqlfiddle.com/#!4/480e2/11

Answer 2

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

Answer 3

I think you are looking for a mysql specific answer. Keep in mind that the syntax could vary across different data stores.

MySQL has a feature that makes this easy.

SELECT Rel_ID, GROUP_CONCAT(Name SEPARATOR ' ') As Names FROM Item GROUP BY Rel_ID;

that should work :-)