Issue with trigger for archiving - sql

Question

Trying to make a trigger that puts data into an archive table when a column called COMPLETION_STATUS goes from incomplete to complete, the dbms is a placeholder for the insert but I'm getting the following errors in the if statement
Error(6,1): PLS-00103: Encountered the symbol enter code here"SELECT" when expecting one of the following: begin function pragma procedure subtype type current cursor delete exists prior The symbol "begin" was substituted for "SELECT" to continue.
Error(9,1): PLS-00103: Encountered the symbol "IF" when expecting one of the following: * & - + ; / at for mod remainder rem and or group having intersect minus order start union where connect || multiset The symbol ";" was substituted for "IF" to continue.
Error(13,4): PLS-00103: Encountered the symbol "end-of-file" when expecting one of the following: ( begin case declare end exception exit for goto if loop mod null pragma raise return select update while with << continue close current delete fetch lock insert open rollback savepoint set sql execute commit forall merge pipe purge
Code:
create or replace TRIGGER ARCHIVING_TRIG
BEFORE UPDATE OF COMPLETION_STATUS ON PROJECT_DATA
BEGIN
DECLARE COMPLETION_STATUS1 VARCHAR2(9);
SELECT COMPLETION_STATUS into COMPLETION_STATUS1
FROM PROJECT_DATA WHERE COMPLETION_STATUS = 'complete'
IF COMPLETION_STATUS1 = 'complete'
THEN
DBMS.output('123');
END IF;
END;

Answer 1

The DECLARE block should be before the BEGIN block.
The SELECT ... statement needs to be terminated with a semicolon (;).
It's dbms_output.put_line() not dbms.output();
You're trying to assign the result of a query that potentially can return more than one row to a scalar variable.
The rows selected from project_data have no relation to the one(s) that triggered the trigger.
I suggest you use something like:
CREATE TRIGGER archiving_trig
AFTER UPDATE
ON project_data
FOR EACH ROW
WHEN (old.completion_status <> 'complete'
AND new.completion_status = 'complete')
BEGIN
dbms_output.put_line('Trigger fired for ID ' || :new.id);
END;
db<>fiddle
I think maybe AFTER is the better time, because you want to archive the row after the status was successfully changed.
Because of the WHEN the trigger will only fire if completion_status has been changed from something other than 'complete' to 'complete'. But you maybe also need to have a method of removing entries from the archive when the status changes from 'complete' to something else. That isn't covered here.
Declaring it as FOR EACH ROW let's you access the values of the updated row via :new. That way you don't need a query to select that nor a variable to select into.

Answer 2

I guess you need this:
create table PROJECT_DATA_NEW as select * from PROJECT_DATA where 1=2;
CREATE OR REPLACE TRIGGER ARCHIVING_TRIG
AFTER UPDATE
ON PROJECT_DATA
FOR EACH ROW
DECLARE
status number;
BEGIN
status:=0;
select 1 into status from PROJECT_DATA where
:new.COMPLETION_STATUS='complete' and
:old.COMPLETION_STATUS='incomplete'
if (status=1) then
insert into PROJECT_DATA_NEW values(:old.column1,
:old.column2,
:old.column3,
:old.column4,
:old.column5,....etc);
end if;
END;
/