How to group using exists - sql

Question

I have the following table
personid talent
1 swim
2 play
1 play
1 swim
2 play
3 swim
3 swim
2 play
So person 1 can both swim and play. Person 2 can only play. Person 3 can only swim.
I need to get the following result
personid talent
1 both
2 play
3 swim
How can I do this using exists ?
I tried
SELECT DISTINCT personid,
CASE WHEN (EXISTS(
SELECT * FROM mytable
-- I got stuck
PS : I have a long solution that works . . But i do not like it because it is long
SELECT DISTINCT dis2.personid , CASE WHEN talcount = 2 THEN 'both'
ELSE talent END AS talent
FROM
(
SELECT personid , COUNT(talent) talcount
FROM
(
SELECT DISTINCT personid , talent
FROM my_table
) AS dis
GROUP BY personid
) dis2
JOIN my_table dis3
ON dis2.personid = dis3.personid

Answer 1

Do you really need to use EXISTS?
SELECT
personid,
CASE
WHEN COUNT(DISTINCT talent) = 2 THEN 'both'
ELSE MIN (talent)
END
FROM talents
GROUP BY personid

Answer 2

You could use the WITH clause to achieve the same effect:
WITH
DISTINCT_TALENTS(PERSONID, TALENT) AS
(SELECT DISTINCT PERSONID, TALENT
FROM TALENTS)
SELECT DISTINCT PERSONID, TALENT
FROM
(SELECT A.PERSONID,
CASE WHEN TALENT_COUNT = 2 THEN 'BOTH' ELSE A.TALENT END
FROM
DISTINCT_TALENTS A
INNER JOIN
(SELECT PERSONID, COUNT(TALENT) TALENT_COUNT
FROM DISTINCT_TALENTS
GROUP BY PERSONID) B
ON A.PERSONID = B.PERSONID)
First you create a virtual DISTINCT_TABLES table:
+------------------+
| personid talent |
+------------------+
| 1 play |
| 1 swim |
| 2 play |
| 3 swim |
+------------------+
next you create a subquery b with the following
+------------------------+
| personid talent_count |
+------------------------+
| 1 2 |
| 2 1 |
| 3 1 |
+------------------------+
you join with original DISTINCT_TALENTS to obtain
+----------+--------+--------------+
| personid | talent | talent_count |
+----------+--------+--------------+
| 1 | both | 2 |
| 1 | both | 2 |
| 2 | play | 1 |
| 3 | swim | 1 |
+----------+--------+--------------+
you take the distinct personid, talent to obtain the final result.
A solution similar to using exists is:
SELECT DISTINCT PERSONID, TALENT
FROM
(
SELECT
B.PERSONID,
CASE
WHEN A.TALENT IS NULL THEN 'swim'
WHEN B.TALENT IS NULL THE 'play'
ELSE 'both'
END TALENT
FROM
TALENTS A
FULL OUTER JOIN
TALENTS B
ON A.PERSONID = B.PERSONID
AND A.TALENT='play'
AND B.TALENT='swim'
)
And finally, also with the EXISTS function used like a lookup function:
SELECT DISTINCT PERSONID, TALENT
FROM (
SELECT A.PERSONID,
CASE
WHEN A.TALENT = 'play' AND EXISTS (SELECT 1 FROM TALENTS B WHERE A.PERSONID = B.PERSONID AND B.TALENT = 'swim')
THEN 'both'
WHEN A.TALENT = 'swim' AND EXISTS (SELECT 1 FROM TALENTS B WHERE A.PERSONID = B.PERSONID AND B.TALENT = 'play')
THEN 'both'
ELSE
A.TALENT
END TALENT
FROM
TALENTS A)