Encountered the symbol "SELECT" when expecting one of the following: - oracle

Question

i need help from you guys.
I am using oracle apex for university, and my task is to create triggers. I'm struggling a lot creating them, I don't even know what is wrong with this trigger. Can someone help me?
I get error
Encountered the symbol "SELECT" when expecting one of the following: ( - + case mod new not null <an identifier> <a double-quoted delimited-identifier> <a bind variable> continue avg count current exists max min prior sql stddev sum variance execute forall merge time timestamp interval date <a string literal with character set specification> <a number> <a single-quoted SQL string> pipe <an alternatively-quoted string literal with character set specification> <an alternat
Error at line 3: PLS-00049: bad bind variable 'NEW'
Error at line 3: PLS-00103: Encountered the symbol "" when expecting one of the following: . ( * # % & = - + ; < / > at for in is mod remainder not rem <an exponent (**)> <> or != or ~= >= <= <> and or like like2 like4 likec between group having intersect minus order start union where connect || indicator multiset member submultiset
Error at line 3: PLS-00049: bad bind variable 'CONTRACT' Error at line 3: PLS-00049: bad bind variable 'CONTRACT' -
CREATE OR REPLACE TRIGGER restrict_orders
BEFORE INSERT ON orders
FOR EACH ROW
BEGIN
DECLARE countOrders number;
set countOrders := SELECT count(contract) FROM orders WHERE :new:contract := old:contract AND (:old.status := 'PREPARING' OR :old.status := 'IN PROGRESS');
IF (countOrders :> 3)
THEN
RAISE_APPLICATION_ERROR (-20202, 'You have too much active orders.');
END IF;
END;

Answer 1

Quite a few errors; see if this helps.
Sample table:
SQL> select * From orders;
CONTRACT STATUS
---------- ---------
1 PREPARING
Trigger:
SQL> CREATE OR REPLACE TRIGGER restrict_orders
2 BEFORE INSERT ON orders
3 FOR EACH ROW
4 DECLARE
5 countOrders number;
6 BEGIN
7 SELECT count(contract)
8 INTO countOrders
9 FROM orders
10 WHERE contract = :new.contract
11 AND status IN ('PREPARING', 'IN PROGRESS');
12
13 IF countOrders > 3 THEN
14 RAISE_APPLICATION_ERROR (-20202, 'You have too many active orders.');
15 END IF;
16 END;
17 /
Trigger created.
Testing:
SQL> insert into orders (contract, status) values (1, 'PREPARING');
1 row created.
SQL> insert into orders (contract, status) values (1, 'PREPARING');
1 row created.
SQL> insert into orders (contract, status) values (1, 'PREPARING');
1 row created.
SQL> insert into orders (contract, status) values (1, 'PREPARING');
insert into orders (contract, status) values (1, 'PREPARING')
*
ERROR at line 1:
ORA-20202: You have too many active orders.
ORA-06512: at "SCOTT.RESTRICT_ORDERS", line 11
ORA-04088: error during execution of trigger 'SCOTT.RESTRICT_ORDERS'
Kind of works. However, note that it'll fail if you attempt to insert more than a single row at a time because table will be mutating (so you'd have to take another, more complex approach), but - if you'll insert just one row at a time, you're good:
SQL> insert into orders (contract, status)
2 select 1, 'PREPARING' from dual union all
3 select 2, 'IN PROGRESS' from dual;
insert into orders (contract, status)
*
ERROR at line 1:
ORA-04091: table SCOTT.ORDERS is mutating, trigger/function may not see it
ORA-06512: at "SCOTT.RESTRICT_ORDERS", line 4
ORA-04088: error during execution of trigger 'SCOTT.RESTRICT_ORDERS'
SQL>

Answer 2

You need to correct your syntax which should be -
CREATE OR REPLACE TRIGGER restrict_orders
BEFORE INSERT ON orders
FOR EACH ROW
DECLARE countOrders number;
BEGIN
SELECT count(contract)
INTO countOrders
FROM orders
WHERE :new.contract = :old.contract
AND :old.status IN ('PREPARING', 'IN PROGRESS');
IF (countOrders >= 3) THEN
RAISE_APPLICATION_ERROR (-20202, 'You have too much active orders.');
END IF;
END;