Trigger created with compilation errors. PL/SQL - oracle

Question

I've been searching for a while how to resolve this issue and couldn't find anything helpful.
Why this trigger is created with compilation errors?
The warning im getting
Warning: Trigger created with compilation errors.
CREATE OR REPLACE TRIGGER peope_in_dept
AFTER INSERT OR DELETE OR UPDATE on emp
FOR EACH ROW
BEGIN
VARIABLE v NUMBER;
EXECUTE :v := count_people_in_dept(:new.deptno)
IF :v <= 0 or :v >= 10 THEN
raise_application_error(-20000,'Nieodpowiednia liczba pracownikow');
END IF;
END;
/

Answer 1

Syntax errors. Should be
SQL> CREATE OR REPLACE TRIGGER peope_in_dept
2 AFTER INSERT OR DELETE OR UPDATE
3 ON emp
4 FOR EACH ROW
5 DECLARE
6 v NUMBER;
7 BEGIN
8 v := count_people_in_dept (:new.deptno);
9
10 IF v <= 0
11 OR v >= 10
12 THEN
13 raise_application_error (-20000, 'Nieodpowiednia liczba pracownikow');
14 END IF;
15 END;
16 /
Trigger created.
SQL>
However, I suspect it won't work if count_people_in_dept function counts employees in emp table. Why? Because table is mutating:
SQL> UPDATE emp SET comm = 1 WHERE deptno = 10;
UPDATE emp SET comm = 1 WHERE deptno = 10
*
ERROR at line 1:
ORA-04091: table SCOTT.EMP is mutating, trigger/function may not see it
ORA-06512: at "SCOTT.COUNT_PEOPLE_IN_DEPT", line 6
ORA-06512: at "SCOTT.PEOPE_IN_DEPT", line 4
ORA-04088: error during execution of trigger 'SCOTT.PEOPE_IN_DEPT'
SQL>
Now, it depends on what you really are doing in that function. One way out is to set the function to be an autonomous transaction; another one is to use compound trigger; the third option is to use custom type and a package. Or, modify the process altogether (i.e. avoid the trigger).

Answer 2

Why this trigger is created with compilation errors?
Because you are trying to create a SQL/Plus global bind variable inside a PL/SQL procedure and then using EXECUTE rather than just calling the function (and you missed a ; statement terminator).
The correct syntax would be:
FOR EACH ROW
DECLARE
v NUMBER;
BEGIN
v := count_people_in_dept(:new.deptno);
IF v <= 0 or v >= 10 THEN
Then it would compile. However, it still won't work as the table would be mutating as the trigger is running.
Instead, you can use a statement trigger rather than a row trigger:
CREATE OR REPLACE TRIGGER people_in_dept
AFTER INSERT OR DELETE OR UPDATE on emp
DECLARE
v_count PLS_INTEGER;
BEGIN
SELECT 1
INTO v_count
FROM dept d
LEFT OUTER JOIN emp e
ON (e.deptno = d.deptno)
GROUP BY d.deptno
HAVING COUNT(e.deptno) NOT BETWEEN 1 AND 9
FETCH FIRST ROW ONLY;
raise_application_error(-20000,'Nieodpowiednia liczba pracownikow');
EXCEPTION
WHEN NO_DATA_FOUND THEN
-- Do nothing.
NULL;
END;
/
db<>fiddle here
You could also write it as a compound trigger that aggregates the changes in deptno and then only checks the changed values using your function; however, that is a lot more complicated.