Merge many data as one data

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Oracle

I have data like this

CCSKIYEARDOULE | CCSKIYEAR
------------------------------------
92-93                     | 92
92-93                     | 93
94-95                     | 94
94-95                     | 95
96-97                     | 97

But I want the output like this

CCSKIYEARDOULE | CCSKIYEAR
------------------------------------
92-93                     | 92, 93
94-95                     | 94, 95
96-97                     | 97

I already use the group_concat, but I got an error "ORA-00904: "GROUP_CONCAT": invalid identifier"

What I have tried:

SELECT GROUP_CONCAT(CCSKIYEARDOUBLE), CCSKIYEAR FROM CCS2_TBL_KI2 GROUP BY CCSKIYEARDOUBLE ORDER BY CCSKIYEAR ASC;