Looking to throw an error where the value i"m updating is a "not null" value.
For example. In below table, say I wanted to update Paul"s lastname with "Jackson". The SQL should throw an error to say that the value that is being updated is "not null".
You need to do this with a trigger. Example trigger:
create trigger schema.trigger_name
before update of last_name
for each row
if :old.last_name is not null then
raise_application_error (-20100, 'Last name already has a value');
But this will stop any process that is running by raising a plsql error.