how to modify an existing check constraint?

问题

Is there any way to modify an existing check constraint on a table other than dropping and re-creating it?

create table t ( n number);
ora10g> Tabelle wurde erstellt.

ora10g> alter table t add constraint ck check(n>0);

Tabelle wurde geõndert.

ora10g> alter table t modify constraint ck check(n<0);
alter table t modify constraint ck check(n<0)
                                   *
FEHLER in Zeile 1:
ORA-00933: SQL-Befehl wurde nicht korrekt beendet

回答1:

You have to drop it and recreate it, but you don't have to incur the cost of revalidating the data if you don't want to.

alter table t drop constraint ck ;
alter table t add constraint ck check (n < 0) enable novalidate;

The enable novalidate clause will force inserts or updates to have the constraint enforced, but won't force a full table scan against the table to verify all rows comply.

回答2:

Create a new constraint first and then drop the old one.
That way you ensure that:

• constraints are always in place
• existing rows do not violate new constraints
• no illegal INSERT/UPDATEs are attempted after you drop a constraint and before a new one is applied.

回答3:

NO, you can't do it other way than so.

回答4:

No. If such a feature existed it would be listed in this syntax illustration. (Although it's possible there is an undocumented SQL feature, or maybe there is some package that I'm not aware of.)

来源：https://stackoverflow.com/questions/5077658/how-to-modify-an-existing-check-constraint