问题
Is there a way to stack/group string/text per user ?
data I have
USER STATES
1 CA
1 AR
1 IN
2 CA
3 CA
3 NY
4 CA
4 AL
4 SD
4 TX
What I need is
USER STATES
1 CA / AR / IN
2 CA
3 CA / NY
4 CA / AL / SD / TX
I tried cross join and then another cross join however but the data spools out. Thanks!
回答1:
I am not an expert but this should work. You may need to modify it a bit per your exact requirement. Hope this helps!
CREATE VOLATILE TABLE temp AS (
SELECT
USER
,STATES
,ROW_NUMBER() OVER (PARTITION BY USER ORDER BY STATES) AS rn
FROM yourtable
) WITH DATA PRIMARY INDEX(USER) ON COMMIT PRESERVE ROWS;
WITH RECURSIVE rec_test(US,ST, LVL)
AS
(
SELECT USER,STATES (VARCHAR(10)),1
FROM temp
WHERE rn = 1
UNION ALL
SELECT USER, TRIM(STATES) || ', ' || ST,LVL+1
FROM temp INNER JOIN rec_test
ON USER = US
AND temp.rn = rec_test.lvl+1
)
SELECT US,ST, LVL
FROM rec_test
QUALIFY RANK() OVER(PARTITION BY US ORDER BY LVL DESC) = 1;
回答2:
If Teradata's XML-services are installed there's a function named XMLAGG, which returns a similar result: CA, AR, IN
SELECT user,
TRIM(TRAILING ',' FROM (XMLAGG(TRIM(states)|| ',' /* optionally ORDER BY ...*/) (VARCHAR(10000))))
FROM tab
GROUP BY 1
Btw, using recursion will result in huge spool usage, because you keep all the intermediate rows in spool before returning the final row.
回答3:
Unfortunately there is no GROUP_CONCAT or any string aggregate functions in Teradata (at least none that I'm aware of) so one way to achieve your result would be to use recursion, since you don't know the maximum values of states per user.
For recursion you should use a Volatile Table, as OLAP functions are not allowed in the recursive part. This is a non-tested code (I've got no way of testing it unfortunately), so there might be several bugs, but should give you the concept and with some troubleshooting (if needed) give you expected result.
Replace yourtable in definition of Volatile Table with your real table name.
CREATE VOLATILE TABLE vt AS (
SELECT
user
, states
, ROW_NUMBER() OVER (PARTITION BY user ORDER BY states) AS rn
, COUNT(*) OVER (PARTITION BY user) AS cnt
FROM yourtable
) WITH DATA
UNIQUE PRIMARY INDEX(user, rn)
ON COMMIT PRESERVE ROWS;
WITH RECURSIVE cte (user, list, rn) AS (
SELECT
user
, CAST(states AS VARCHAR(1000)) -- maximum size based on maximum number of rows * length of states
, rn
FROM vt
WHERE rn = cnt -- start with last states row
UNION ALL
SELECT
vt.user
, cte.list || ',' || vt.states
, vt.rn
FROM vt
JOIN cte ON vt.user = cte.user AND vt.rn = cte.rn - 1 -- append a row that is rn-1 of your rows for a given user
)
SELECT user, list
FROM cte
WHERE rn = 1; -- going from last to first, in this condition there should be entire list
This solution isn't perfect - it forces the engine to store immediate results in a temporary area during query processing. You may encounter a No more spool space error.
来源：https://stackoverflow.com/questions/35854336/teradata-sql-stack-rows-per-user