3. операторы SQLдля вставки, обновления и удаления данных в таблице Oracle

То есть для всего этого одновременно? MERGE.

Купи или скачай книги по Oracle PL-SQL, и учи.
Без чтения книг не хер лезть в это занятие.
Толку не будет.

--A
CREATE TABLE zamestnanci AS SELECT * FROM hr.employees;

-- B
ALTER TABLE zamestnanci
ADD CONSTRAINT employees_pk PRIMARY KEY (employee_id);

-- C
DESC zamestnanci;

INSERT INTO zamestnanci (employee_id,last_name,email,hire_date,job_id)
VALUES(98,'Rybansky','rybansky',sysdate,'HR_REP');

INSERT INTO zamestnanci (employee_id,last_name,email,hire_date,job_id)
VALUES(99,'Dodatocny','dodatocny',sysdate,'HR_REP');

-- D
UPDATE zamestnanci
SET salary = salary + 0.1 * salary;

-- E
DELETE FROM zamestnanci
WHERE employee_id > 190;

-- F
SELECT * FROM zamestnanci
WHERE salary > 500;

-- G
SELECT * FROM zamestnanci
WHERE department_id = (select department_id from hr.departments where department_name = 'IT');

-- H
SELECT * FROM zamestnanci
WHERE extract(month from hire_date) = 6;

-- I
SELECT first_name, last_name, CONCAT(email,'@ tuke.sk ') from zamestnanci;

Zobrazte meno (first_name), priezvisko (last_name), názov oddelenia (department_name) a dátum nástupu (hire_date) zamestnancov z oddelenia Sales a zoraďte ich podľa dátumu nástupu zostupne.

SELECT COUNT(*) as pocet_zamestnancov, SUBSTR(job_id, 1, 2) as prve_dve_pismena
FROM employees
GROUP BY job_id
HAVING AVG(salary) > 1000;