Question

So a dilemna, I have an Oracle table called T_GROUP. The records in the table have a unique id (ID) and they are part of a Study, identified by STUDY_ID, so multiple groups can be in the same Study.

CREATE TABLE T_GROUP
(
    "ID" NUMBER(10,0),
    "GROUP_NAME" VARCHAR2(255 CHAR),
    "STUDY_ID" NUMBER(10,0)
)

The existing table has hundreds of records and I now add a new column called GROUP_INDEX:

ALTER TABLE T_GROUP ADD (
 GROUP_INDEX NUMBER(10,0) DEFAULT(0)
);

After adding the column I need to run a script to update the GROUP_INDEX field as such: it should start at 1 and increment by 1 for each group within a study, starting with the lowest ID.

So now I have data as follows:

ID  GROUP_NAME      STUDY_ID    GROUP_INDEX
-------------------------------------------
1   Group 1         3           0
2   Group 2         3           0
3   My Group        5           0
4   Big Group       5           0
5   Group X         5           0
6   Group Z         6           0
7   Best Group      6           0

After the update the group_index field should be as follows:

ID  GROUP_NAME      STUDY_ID    GROUP_INDEX
-------------------------------------------
1   Group 1         3           1
2   Group 2         3           2
3   My Group        5           1
4   Big Group       5           2
5   Group X         5           3
6   Group Z         6           1
7   Best Group      6           2

The update will be run from sqlplus via a batch file. I’ve played around with group by and sub queries but I’m not having much luck, and having never used sqlplus I’m not sure if I can use variables, cursors etc. All tips greatly appreciated!

Answer 1

You should be able to use the analytic function row_number for this

UPDATE t_group t1
   SET group_index = (SELECT rnk
                        FROM (SELECT id,
                                     row_number() over (partition by study_id
                                                            order by id) rnk
                                FROM t_group) t2
                       WHERE t2.id = t1.id)