Problem to update 16 rows, it updates all rows in table

Question

I tried to update 16 rows with AL as divion name with the script as below:
Update wire_center a set a.wg_id='63'
where EXISTS (select b.div_name from wire_center a, division b, district c, ns_workgroups d
where B.DIV_NAME='AL' AND a.dis_id=c.dis_id and b.div_id=c.div_id and d.wg_id=a.wg_id );
When I run it, it updates all the rows in the table.
However when I run the select subquery, it returns 16 rows.
It seems where EXISTS is the problem. if I take exists out, it gave me ora-00936 error.
How to fix it? Please need urgent help. db is 10g.
Thanks in advance.

Answer 1

If I understand correctly what you want, you should not include wire_center again in the second select (in your exists clause).
The second select has no relation to the table you are updating, so because the second select returns 16 rows, the exists will always be true. For every row. So every row will be updated.
Instead of
Update wire_center a set a.wg_id='63'
where EXISTS (select b.div_name from wire_center a, division b, district c, ns_workgroups d
where B.DIV_NAME='AL' AND a.dis_id=c.dis_id and b.div_id=c.div_id and d.wg_id=a.wg_id );try this:
Update wire_center a set a.wg_id='63'
where EXISTS (select b.div_name from division b, district c, ns_workgroups d
where B.DIV_NAME='AL' AND a.dis_id=c.dis_id and b.div_id=c.div_id and d.wg_id=a.wg_id );Edited by: theoa on 29-dec-2010 14:27