Errors with identifiers in PL/SQL - oracle

Question

I am trying to run some PL/SQL code but it contains some errors about identifiers plese help me with it. The code is not running
DECLARE
a := customer.purchase%TYPE;
id := &employee.empno;
BEGIN
UPDATE employee SET salary = salary + 5000;
UPDATE employee SET bonus = bonus + 1000 WHERE empno = &id;
SAVEPOINT sumeet;
UPDATE customer SET purchase = purchase + 5000 WHERE custid = a;
SELECT SUM(purchase) INTO a;
IF (a < 11000) THEN
ROLLBACK sumeet;
END IF;
COMMIT;
END;
/

Answer 1

in addition to Alen's fix, instead of the ROLLBACK why don't you do :
UPDATE customer SET purchase = purchase + 5000
WHERE custid = a
AND (select sum(purchase) from customer) + 5000 < 11000;
COMMIT;

Answer 2

1: This is wrong:
DECLARE
a := customer.purchase%TYPE;
id := &employee.empno;
You don't put a := after the variable name, & is invalid, and employee.empno is not a valid data type. i.e.:
DECLARE
a customer.purchase%TYPE;
id employee.empno%TYPE;
2: You don't need & to refer to the id variable:
UPDATE employee SET bonus = bonus + 1000 WHERE empno = &id;
i.e.:
UPDATE employee SET bonus = bonus + 1000 WHERE empno = id;

Answer 3

Here's a tip: Combine your two updates on employee into one.
UPDATE employee
SET salary = salary + 5000,
bonus = bonus + case when empno = &id then 1000 else 0 end;
Also, start using meaningful variable names.

Answer 4

Try with this block, but first change the values (1, 2) in the declaration block.
DECLARE
a customer.purchase%TYPE := 1;
id employee.empno%TYPE := 2;
BEGIN
UPDATE employee SET salary = salary + 5000;
UPDATE employee SET bonus = bonus + 1000 WHERE empno = id;
SAVEPOINT sumeet;
UPDATE customer SET purchase = purchase + 5000 WHERE custid = a;
SELECT SUM(purchase) INTO a FROM customer;
IF (a < 11000) THEN
ROLLBACK sumeet;
END IF;
COMMIT;
END;
/