1-- HR স্কিমা থেকে কর্মচারী তথ্য 2SELECT employee_id, 3 first_name, 4 last_name, 5 salary 6 FROM employees 7 WHERE salary > 5000 8 AND department_id = 60 9 ORDER BY salary DESC 10FETCH FIRST 5 ROWS ONLY;

1-- BETWEEN অপারেটর 2WHERE salary BETWEEN 3000 AND 8000 3-- IN তালিকা 4WHERE dept_id IN (10, 20, 30) 5-- LIKE প্যাটার্ন 6WHERE last_name LIKE 'S%' 7-- NULL চেক 8WHERE commission_pct IS NOT NULL 9-- NOT অপারেটর 10WHERE dept_id NOT IN (40, 50)

SELECT e.first_name, d.department_name FROM employees e INNER JOIN departments d ON e.department_id = d.department_id;

1SELECT department_id, 2 COUNT(*) AS মোট_কর্মচারী, 3 AVG(salary) AS গড়_বেতন, 4 MAX(salary) AS সর্বোচ্চ_বেতন, 5 MIN(salary) AS সর্বনিম্ন_বেতন 6 FROM employees 7 GROUP BY department_id 8HAVING COUNT(*) > 3 9 ORDER BY গড়_বেতন DESC;

1SELECT 2 UPPER('oracle sql'), -- ORACLE SQL 3 LENGTH('বাংলাদেশ'), -- 8 4 SUBSTR('Oracle SQL',8), -- SQL 5 INSTR('hello','l'), -- 3 6 REPLACE('Hi World', 7 'World','SQL'), -- Hi SQL 8 TRIM(' hello '), -- hello 9 LPAD('7',5,'0'), -- 00007 10 CONCAT('Oracle',' SQL') -- Oracle SQL 11FROM dual;

1SELECT 2 SYSDATE AS আজকের_তারিখ, 3 ADD_MONTHS(SYSDATE, 6) AS ছয়_মাস_পরে, 4 LAST_DAY(SYSDATE) AS মাসের_শেষ, 5 EXTRACT(YEAR FROM SYSDATE) AS বছর, 6 EXTRACT(MONTH FROM SYSDATE) AS মাস, 7 MONTHS_BETWEEN( 8 SYSDATE, hire_date) AS কর্মকাল_মাস, 9 TO_CHAR(SYSDATE, 10 'DD-MON-YYYY HH24:MI') AS ফরম্যাট_তারিখ 11FROM employees;

1-- TO_CHAR: তারিখ ফরম্যাট 2SELECT TO_CHAR(SYSDATE, 3 'DD/MM/YYYY') -- 07/04/2026 4FROM dual; 5-- TO_DATE: স্ট্রিং থেকে তারিখ 6SELECT TO_DATE('15-01-2026', 7 'DD-MM-YYYY') 8FROM dual; 9-- NVL ও COALESCE 10SELECT 11 NVL(commission_pct, 0), 12 NVL2(commission_pct, 13 salary * commission_pct, 14 0) AS কমিশন, 15 COALESCE(phone, mobile, 16 'যোগাযোগ নেই') AS যোগাযোগ 17FROM employees;

1SELECT 2 first_name, 3 department_id, 4 salary, 5 RANK() OVER ( 6 PARTITION BY department_id 7 ORDER BY salary DESC 8 ) AS dept_rank, 9 SUM(salary) OVER ( 10 PARTITION BY department_id 11 ) AS dept_total, 12 LAG(salary, 1, 0) OVER ( 13 ORDER BY hire_date 14 ) AS পূর্ববর্তী_বেতন, 15 ROUND(100 * salary / 16 SUM(salary) OVER(), 2) AS শতকরা 17FROM employees 18ORDER BY department_id, dept_rank;

1-- গড়ের চেয়ে বেশি বেতন পায় 2SELECT first_name, salary 3 FROM employees 4 WHERE salary > ( 5 SELECT AVG(salary) 6 FROM employees 7 ) 8 ORDER BY salary DESC;

1-- প্রতি বিভাগের সর্বোচ্চ বেতনধারী 2SELECT first_name, salary, 3 department_id 4 FROM employees e 5 WHERE salary = ( 6 SELECT MAX(salary) 7 FROM employees 8 WHERE department_id 9 = e.department_id 10 );

1CREATE TABLE students ( 2 student_id NUMBER(6) 3 GENERATED ALWAYS 4 AS IDENTITY 5 PRIMARY KEY, 6 full_name VARCHAR2(100) 7 NOT NULL, 8 email VARCHAR2(150) 9 UNIQUE, 10 enroll_date DATE 11 DEFAULT SYSDATE, 12 gpa NUMBER(3,2) 13 CHECK (gpa 14 BETWEEN 0 AND 4) 15);

1-- কলাম যোগ করা 2ALTER TABLE students 3 ADD phone VARCHAR2(20); 4-- কলাম পরিবর্তন 5ALTER TABLE students 6 MODIFY full_name VARCHAR2(200); 7-- কলাম মুছে ফেলা 8ALTER TABLE students 9 DROP COLUMN phone; 10-- টেবিল মুছে ফেলা 11DROP TABLE students; 12-- দ্রুত ডেটা মুছা 13TRUNCATE TABLE students;

1-- B-Tree index (ডিফল্ট) 2CREATE INDEX idx_emp_lname 3 ON employees (last_name); 4-- Composite index 5CREATE INDEX idx_emp_dept_sal 6 ON employees ( 7 department_id, 8 salary 9 ); 10-- Function-based index 11CREATE INDEX idx_upper_lname 12 ON employees (UPPER(last_name)); 13-- Execution Plan দেখা 14EXPLAIN PLAN FOR 15 SELECT * FROM employees 16 WHERE last_name = 'King'; 17 18SELECT * FROM 19 TABLE(DBMS_XPLAN.DISPLAY);