Re: SQL Challenge: Arbitrary Cross-tab

Josh Berkus wrote:

>Folks,
>
>I have a wierd business case. Annoyingly it has to be written in *portable*
>SQL92, which means no arrays or custom aggregates. I think it may be
>impossible to do in SQL which is why I thought I'd give the people on this
>list a crack at it. Solver gets a free drink/lunch on me if we ever meet at
>a convention.
>
>
>
Might be possible. Would certainly be ugly.

>The Problem: for each "case" there are from zero to eight "timekeepers"
>authorized to work on the "case", out of a pool of 150 "timekeepers". This
>data is stored vertically:
>
>authorized_timekeepers:
>case_id | timekeeper_id
>213447 | 047
>132113 | 021
>132113 | 115
>132113 | 106
>etc.
>
>But, a client's e-billing application wants to see these timekeepers displayed
>in the following horizontal format:
>
>case_id | tk1 | tk2 | tk3 | tk4 | tk5 | tk6 | tk7 | tk8
>213447 | 047 | | | | | | | |
>132113 | 021 | 115 | 106 | 034 | 109 | 112 | 087 |
>etc.
>
>Order does not matter for timekeepers 1-8.
>
>This is a daunting problem because traditional crosstab solutions do not work;
>timekeepers 1-8 are coming out of a pool of 150.
>
>Can it be done? Or are we going to build this with a row-by-row procedural
>loop? (to reiterate: I'm not allowed to use a custom aggregate or other
>PostgreSQL "advanced feature")
>
>
>
If it can be done, it might be extremely ugly. I am thinking a massive
set of left self joins (since there could be between 0 and 8).

Something like:
select case_id FROM authorized_timekeeper t0
LEFT JOIN
(SELECT case_id, min(timekeeper_id) FROM authorized_timekeeper
GROUP BY case_id) t1
ON case_id
LEFT JOIN
(SELECT case_id, min(timekeeper_id) FROM authorized_timekeeper
WHERE timekeeper_id <> t1.timekeeper
GROUP BY case_id) t2
ON case_id
LEFT JOIN
(SELECT case_id, min(timekeeper_id) FROM authorized_timekeeper
WHERE timekeeper_id NOT IN (t1.timekeeper, t2.timekeeper)
GROUP BY case_id) t3
etc....

If this is not an option, instead I would create a series of views.
Something like:
CREATE VIEW t1 AS select case_id, min(timekeeper_id) AS tk_id
from authorized_timekeepers
group by case_id;
CREATE VIEW t2 AS select case_id, min(timekeeper_id) AS tk_id
from authorized_timekeepers
WHERE tk_id NOT IN (SELECT tk_id FROM t1)
group by case_id;
CREATE VIEW t3 AS select case_id, min(timekeeper_id) AS tk_id
FROM authorized_timekeepers
WHERE tk_id NOT IN (SELECT tk_id FROM t1)
AND tk_id NOT IN (SELECT tk_id FROM t2)
GROUP BY case_id;
Etc.
Then you do a left join among the views.

Hope that this helps.

Best Wishes,
Chris Travers