DDL, DML, PL/SQL touchpoints, joins, and tuning reminders target Oracle-specific interviews and operations. The Oracle roadmap frames the same skills as a progression from writing queries to managing performance.

Oracle / database learning roadmap — SQL and Oracle ecosystem skills sequenced for learners and professionals.

Oracle SQL Cheatsheet

Quick reference guide for Oracle database operations

Introduction to SQL

SQL (Structured Query Language) is the standard language for managing relational databases.

SQL Command Types
  • DDL: Data Definition Language (CREATE, ALTER, DROP)
  • DML: Data Manipulation Language (INSERT, UPDATE, DELETE)
  • DQL: Data Query Language (SELECT)
  • DCL: Data Control Language (GRANT, REVOKE)
  • TCL: Transaction Control Language (COMMIT, ROLLBACK)
Basic Example
SELECT * FROM customers 
WHERE country = 'USA' 
ORDER BY last_name 
FETCH FIRST 10 ROWS ONLY;

Setting Up Oracle Environment

Installation
  • Oracle Database Express Edition (XE)
  • SQL Developer (GUI)
  • Oracle Instant Client
Online Tools
  • Oracle Live SQL
  • DB Fiddle (Oracle mode)
  • SQL Fiddle (Oracle mode)
IDEs
  • Oracle SQL Developer
  • TOAD for Oracle
  • PL/SQL Developer
  • DBeaver

Schema and Table Operations

User/Schema Creation
CREATE USER my_user IDENTIFIED BY password;
GRANT CONNECT, RESOURCE TO my_user;
ALTER SESSION SET CURRENT_SCHEMA = my_user;
Table Creation
CREATE TABLE employees (
  id NUMBER PRIMARY KEY,
  name VARCHAR2(100) NOT NULL,
  email VARCHAR2(100) UNIQUE,
  hire_date DATE DEFAULT SYSDATE,
  salary NUMBER(10,2) CHECK (salary > 0)
);

CREATE SEQUENCE emp_seq START WITH 1;
Common Data Types
  • NUMBER: Numeric values
  • VARCHAR2(n): Variable string
  • DATE: Date and time
  • TIMESTAMP: Precise date/time
  • CHAR(n): Fixed-length string
  • CLOB: Large text data

Basic SQL Queries

Filtering Data
SELECT product_name, price
FROM products
WHERE price > 100 
  AND category = 'Electronics'
ORDER BY price DESC
FETCH FIRST 5 ROWS ONLY;
Sorting & Limiting
SELECT * FROM customers
ORDER BY last_name ASC, 
         first_name ASC
OFFSET 20 ROWS FETCH NEXT 10 ROWS ONLY;

Modifying Data (DML)

INSERT
INSERT INTO employees 
(id, name, email, salary)
VALUES 
(emp_seq.NEXTVAL, 'John Doe', 'john@example.com', 50000);
UPDATE
UPDATE employees
SET salary = salary * 1.1
WHERE department = 'Sales';
DELETE
DELETE FROM products
WHERE discontinued = 1;

Advanced Filtering

IN, BETWEEN, LIKE
SELECT * FROM products
WHERE category IN ('Electronics', 'Books')
  AND price BETWEEN 50 AND 200
  AND product_name LIKE '%Phone%';
NULL Handling
SELECT * FROM customers
WHERE phone IS NOT NULL;

UPDATE employees
SET manager_id = NULL
WHERE manager_id = 10;

Working with Multiple Tables

INNER JOIN
SELECT o.order_id, c.customer_name
FROM orders o
INNER JOIN customers c 
  ON o.customer_id = c.customer_id;
LEFT JOIN
SELECT e.name, d.department_name
FROM employees e
LEFT JOIN departments d
  ON e.dept_id = d.dept_id;
Self Join Example
SELECT e1.name AS employee, 
       e2.name AS manager
FROM employees e1
LEFT JOIN employees e2
  ON e1.manager_id = e2.employee_id;

Aggregation and Grouping

Aggregate Functions
SELECT 
  COUNT(*) AS total_products,
  AVG(price) AS avg_price,
  MIN(price) AS min_price,
  MAX(price) AS max_price,
  SUM(stock) AS total_stock
FROM products;
GROUP BY & HAVING
SELECT department_id, 
  COUNT(*) AS emp_count,
  AVG(salary) AS avg_salary
FROM employees
GROUP BY department_id
HAVING COUNT(*) > 5
ORDER BY avg_salary DESC;
Key Differences
  • WHERE filters before grouping
  • HAVING filters after grouping
  • Non-aggregated columns in SELECT must be in GROUP BY
  • Aggregate functions can't be used in WHERE

Subqueries

Single-Row Subquery
SELECT name, salary
FROM employees
WHERE salary > (
  SELECT AVG(salary)
  FROM employees
);
Multi-Row Subquery
SELECT product_name, price
FROM products
WHERE category_id IN (
  SELECT category_id
  FROM categories
  WHERE department = 'Electronics'
);
Correlated Subquery
SELECT e.name, e.salary, e.department_id
FROM employees e
WHERE salary > (
  SELECT AVG(salary)
  FROM employees
  WHERE department_id = e.department_id
);

Views and Indexes

Creating Views
CREATE OR REPLACE VIEW high_paid_employees AS
SELECT id, name, salary, department
FROM employees
WHERE salary > 100000
WITH CHECK OPTION;

SELECT * FROM high_paid_employees;
Creating Indexes
CREATE INDEX idx_employee_name 
ON employees(name);

CREATE UNIQUE INDEX idx_customer_email
ON customers(email);

CREATE INDEX idx_order_dates
ON orders(order_date, shipped_date);
Index Best Practices
  • Index columns frequently used in WHERE, JOIN, ORDER BY
  • Avoid over-indexing (slows down INSERT/UPDATE)
  • Consider composite indexes for multi-column queries
  • Monitor index usage and remove unused indexes

Basic SQL Functions

String Functions
SELECT 
  first_name || ' ' || last_name AS full_name,
  UPPER(email) AS email_upper,
  SUBSTR(phone, 1, 3) AS area_code,
  LENGTH(address) AS addr_length
FROM customers;
Date Functions
SELECT 
  SYSDATE AS current_datetime,
  TRUNC(order_date) AS order_date_only,
  due_date - SYSDATE AS days_remaining,
  ADD_MONTHS(hire_date, 12) AS anniversary
FROM orders;
Math Functions
SELECT 
  ROUND(price * 1.1, 2) AS price_with_tax,
  ABS(discount) AS absolute_discount,
  MOD(quantity, 10) AS remainder,
  CEIL(weight) AS rounded_weight
FROM products;

Transactions and ACID

Transaction Control
SET TRANSACTION NAME 'FundsTransfer';

UPDATE accounts 
SET balance = balance - 100
WHERE id = 123;

UPDATE accounts 
SET balance = balance + 100
WHERE id = 456;

COMMIT;
-- or ROLLBACK if error occurs
ACID Properties
  • Atomicity: All or nothing execution
  • Consistency: Valid state transitions
  • Isolation: Concurrent transactions don't interfere
  • Durability: Committed changes persist

PL/SQL Procedures & Functions

Stored Procedure
CREATE OR REPLACE PROCEDURE update_salary(
  emp_id IN NUMBER,
  increase_percent IN NUMBER
)
AS
BEGIN
  UPDATE employees
  SET salary = salary * (1 + increase_percent/100)
  WHERE id = emp_id;
  
  COMMIT;
END;
/

EXEC update_salary(101, 10);
PL/SQL Function
CREATE OR REPLACE FUNCTION get_employee_age(
  emp_id IN NUMBER
) RETURN NUMBER
AS
  age NUMBER;
BEGIN
  SELECT FLOOR(MONTHS_BETWEEN(SYSDATE, birth_date)/12)
  INTO age
  FROM employees
  WHERE id = emp_id;
  
  RETURN age;
END;
/

SELECT name, get_employee_age(id) AS age
FROM employees;

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Quick reference guide

Comprehensive Oracle SQL Cheatsheet & Examples Cheatsheet Reference

This Oracle SQL Cheatsheet & Examples cheatsheet on Nikhil Learn Hub collects syntax, commands, and practical snippets for quick revision. Learn Oracle SQL with commands, queries, syntax, examples, and best practices for beginners and developers.

Use the reference cards and examples above during coding sessions; return here instead of scattered searches when you need dependable reminders. Follow the Oracle / database learning roadmap when you want structured lessons beyond one-page lookups.

Quick lookup coverage

  • Syntax, commands, and API signatures
  • Copy-ready examples and common patterns
  • Terminology for coursework and interviews
  • Cross-links to the matching learning roadmap

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  • Security, performance, or scale cautions
  • Integration with adjacent stacks on this site
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