The trick with triggers

Creating triggers, prior to 11g, would default them to an enabled state.

From 11g, we have this in the documentation:

By default, a trigger is created in enabled state. To create a trigger in disabled state, use the DISABLE clause of the CREATE TRIGGER statement.

So when I write my DDL scripts, given this behaviour, I know what I'd prefer:

SQL> create table test_table(a number);
table TEST_TABLE created.
create or replace trigger test_trigger_good before insert on test_table for each row DISABLE
begin
  null -- missing semicolon
end;
/
TRIGGER test_trigger_good compiled
Warning: execution completed with warning

SQL> insert into test_table (a) values (1);

1 rows inserted.

or

SQL> create or replace trigger test_trigger_bad before insert on test_table for each row 
begin
  null -- missing semicolon
end;
/
TRIGGER test_trigger_bad compiled
Warning: execution completed with warning

SQL> insert into test_table (a) values (1);

SQL Error: ORA-04098: trigger 'DEVMGR.TEST_TRIGGER_BAD' is invalid and failed re-validation
04098. 00000 -  "trigger '%s.%s' is invalid and failed re-validation"
*Cause:    A trigger was attempted to be retrieved for execution and was
           found to be invalid.  This also means that compilation/authorization
           failed for the trigger.
*Action:   Options are to resolve the compilation/authorization errors,
           disable the trigger, or drop the trigger.

Only run this when you know things are cool, ie - the triggers does not have compilation errors.

alter trigger test_trigger_good enable;

Otherwise you get the same problem, since you can enable an invalid trigger.

Tip of the hat to Connor McDonald for suggesting this many moons ago.