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Question

Hi,
I need to perform an update on a table like this:
update myTable
set myColumn = ltrim(myColumn, '0'); --trim all leading zeros
I wnat this to perform on every row where it does not conflict with my unique constraint. I do not want to disable the constrataint because then I will end up with dupplicate records.
Is it possible to create a script where the query executes on all rows where it does not conflict with any constrain? ...and simpy skip the confliction-rows?
Thanks!
(Oracle 10g)

Answer 1

how shall i wite the query if I want to take the myOtherColumn into consideration? Following version should capture all possibilities (also when the trimmed pk is already there):
SQL>  create table mytable (mycolumn, myothercolumn, mysecondothercolumn)
as
-- select '1', 'x' , 'y' from dual union all
select '01', 'x' , 'y' from dual union all
select '001', 'x', 'y2' from dual
Table created.
SQL>  alter table mytable add constraint mytable_pk primary key (mycolumn, myothercolumn)
Table altered.
SQL>  select * from mytable
MYC M MY
01  x y
001 x y2
2 rows selected.
SQL>  update mytable t1
   set mycolumn = ltrim (mycolumn, '0')
where rowid in (select max (rowid)
                   from mytable t2
                   group by ltrim (mycolumn, '0'),myothercolumn
                 having count (ltrim (mycolumn, '0')) > 1)
    and not exists (select null from mytable t2 where t2.mycolumn = ltrim(t1.mycolumn,0) and t1.myothercolumn=t2.myothercolumn)
1 row updated.
SQL>  select * from mytable
MYC M MY
01  x y
1   x y2
2 rows selected.