Constraint with condition?

Question

I need some help with creating some sort of a constraint or check on a table row.
I have the following table:
create table mytable
o_no number null,
o_name varchar2(255) null,
type char(1) not null,
valid char(1) not null
alter table mytable add constraint c_typ_1 check (type in('O', 'S'));
alter table mytable add constraint c_valid_1 check (valid in('N', 'Y'));
Now I need a constraint for having a unique 'o_no' and 'o_name' only if the type is 'O' and the valid state is 'Y'.
Is there a way with a constraint? If not, how can I solve with?
Thanks,
Rainer

Answer 1

Just to expand on Jens' suggestion to use a function-based index, the expressions would be either of:
create unique index mytable_ndx on mytable(
  decode(type, 'O', decode(valid, 'Y', o_no, null), null),
  decode(type, 'O', decode(valid, 'Y', o_name, null), null));
create unique index mytable_ndx on mytable(
  case when type = 'O' and valid = 'Y' then o_no end,
  case when type = 'O' and valid = 'Y' then o_name end);Note though that this will not prevent multiple NULL entries for o_no/o_name given type = 'O' and valid = 'Y'.
Also, the column named TYPE may give you difficulties at some point given that that name is a PL/SQL reserved word.