SQL select group by Query

Question

Suppose a table T1 has 2 columns C1 and C2 and data as follows:
C1 C2
== ==
1 A1
1 A2
2 B1
2 B2
2 B3
3 C1
4 D1
4 D2
I want to write a SQL query to select data and display as follows (i.e. grouped by C1, but C2 should display as single field with say '-' seperator):
C1 C2-Details
== ========
1 A1-A2
2 B1-B2-B3
3 C1
4 D1-D2
Please help.
Thanks in advance
Goli

Answer 1

Your query maybe like this
SELECT c1,
LTRIM(MAX(SYS_CONNECT_BY_PATH(c2,'-'))
KEEP (DENSE_RANK LAST ORDER BY curr),'-') AS employees
FROM (SELECT c1,
c2,
ROW_NUMBER() OVER (PARTITION BY c1 ORDER BY c2) AS curr,
ROW_NUMBER() OVER (PARTITION BY c1 ORDER BY c2) -1 AS prev
FROM t1)
GROUP BY c1
CONNECT BY prev = PRIOR curr AND c1 = PRIOR c1
START WITH curr = 1;