Master SQL Effortlessly: Powerful Handwritten Notes

Introduction:

Master SQL Effortlessly: Powerful Handwritten Notes for Success :

SQL is one of the important thing in the branch of computer science.

SQL is one of the fundamental tools in the database management system. It is widely used for handling and manipulating the data.

It provides secure access control for different users.

If you build any kind of online application, you must need the Database Management System to store and retrieve the data.

It plays an pivot role in storing data securely for application like transactions, etc.

Why are handwritten notes helpful for learning SQL ?

It undergoes multiple aspects like

Easy understanding of Syntax

It makes it easier for users to understand the content easily and efficiently.

In the tech industry, SQL is very essential as the role is as database administrator.

It feels better to the user if we compare the computer-generated and the handwritten notes.

Handwritten notes have a higher chance of getting remembered easily and somehow feel easier to the user.

Contents Included in SQL:

Introduction to SQL

Database concepts

Datatypes

SQL Commands

Constraints

SQL Clauses

Joins and Relationships

Indexes and Optimization

Subqueries and Nested Queries

Views and Stored Procedures

Transaction & ACID Properties

Triggers

Functions & Operators

Normalisation

Cloud Based SQL Services

1. SQL Basics: Understanding the Fundamentals

SQL stands for Structured Query Language.
It is used to communicate with and manage relational databases.
SQL allows you to perform operations like retrieving, updating, and deleting data.

2. SQL Syntax: Structure and Rules

SQL syntax is not case-sensitive, but it’s a good practice to write keywords in uppercase.
Every SQL statement ends with a semicolon (;), especially in complex queries.

3. SELECT Statement: Retrieving Data

The SELECT statement is used to query data from a database.
Basic syntax:SELECT column1, column2 FROM table_name;
Use * to select all columns: SELECT * FROM table_name;

4. WHERE Clause: Filtering Data

The WHERE WHEREclause filters records based on specific conditions.
Syntax:SELECT column1 FROM table_name WHERE condition;
Example:SELECT * FROM Employees WHERE age > 30;

5. AND, OR, NOT Operators

Combine multiple conditions using AND, OR, and NOT.
Example:SELECT * FROM Employees WHERE age > 30 AND department = 'Sales';

6. ORDER BY Clause: Sorting Data

ORDER BYSorting query results in ascending (ASC) or descending (DESC) order.
Example:SELECT * FROM Employees ORDER BY salary DESC;

7. DISTINCT Keyword: Removing Duplicates

Use DISTINCT to remove duplicate values from the results.
Example:SELECT DISTINCT city FROM Employees;

8. Aggregate Functions: Summarizing Data

Common aggregate functions: COUNT(), SUM(), AVG(), MAX(), MIN().
Example:SELECT COUNT(*) FROM Employees;

9. GROUP BY Clause: Grouping Data

GROUP BYGroup rows that have the same values into summary rows.
Example:SELECT department, COUNT(*) FROM Employees GROUP BY department;

10. HAVING Clause: Filtering Groups

HAVINGIt isUsed to filter groups formedBY
Example:SELECT department, AVG(salary) FROM Employees GROUP BY department HAVING AVG(salary) > 50000;

11. JOIN Operations: Combining Tables

INNER JOINReturns records with matching values in both tables.
LEFT JOIN Returns all records from the left table and matching records from the right.
Example:SELECT Employees.name, Departments.department_name FROM Employees INNER JOIN Departments ON Employees.department_id = Departments.department_id;

12. INNER JOIN: Retrieving Data from Multiple Tables

Returns only the matching rows between two tables.
Example:SELECT Orders.id, Customers.name FROM Orders INNER JOIN Customers ON Orders.customer_id = Customers.id;

13. LEFT JOIN: Including Non-Matching Records

Returns all records from the left table and matched records from the right.
Example:SELECT Students.name, Courses.name FROM Students LEFT JOIN Courses ON Students.id = Courses.student_id;

14. RIGHT JOIN: Complementing LEFT JOIN

Returns all records from the right table and matched records from the left.
Example:SELECT Employees.name, Projects.project_name FROM Employees RIGHT JOIN Projects ON Employees.id = Projects.employee_id;

15. FULL JOIN: Returning All Records

Combines and.LEFT JOINRIGHT JOIN Returns all rows from both tables.
Example:SELECT A.name, B.address FROM A FULL JOIN B ON A.id = B.id;

16. Self JOIN: Joining a Table with Itself

A self-joinSELF JOINIt iswhen a table is joined with itself.
Example:SELECT A.name, B.manager_name FROM Employees A, Employees B WHERE A.manager_id = B.id;

17. Subqueries: Querying Inside a Query

A subquery is a query nested inside another query.
Example:SELECT name FROM Employees WHERE department_id = (SELECT id FROM Departments WHERE name = 'HR');

18. INSERT INTO: Adding Data to Tables

Used to insert new rows into a table.
Syntax:INSERT INTO table_name (column1, column2) VALUES (value1, value2);

19. UPDATE: Modifying Data

Used to modify existing records in a table.
Syntax:UPDATE table_name SET column1 = value1 WHERE condition;
Example:UPDATE Employees SET salary = 50000 WHERE department = 'HR';

20. DELETE: Removing Data

Used to delete rows from a table.
Syntax:DELETE FROM table_name WHERE condition;
Example:DELETE FROM Employees WHERE id = 5;

21. Constraints: Ensuring Data Integrity

Constraints like PRIMARY KEY, FOREIGN KEY, NOT NULL, and UNIQUE ensure data validity.
Example:CREATE TABLE Employees (id INT PRIMARY KEY, name VARCHAR(100) NOT NULL);

22. Primary Key: Unique Identifier for Rows

A unique idenAn identifierPRIMARY KEY Identifies each row in a table.
Example:CREATE TABLE Students (student_id INT PRIMARY KEY, name VARCHAR(100));

23. Foreign Key: Relating Tables

A⁣FOREIGN KEY creates a relationship between two tables. tablExample:
ple: CREATE TABLE Orders (order_id INT, customer_id INT, FOREIGN KEY (customer_id) REFERENCES Customers(customer_id));

24. Not Null Constraint: Preventing Null Values

Ensures a column cannot have a NULL value.
Example:CREATE TABLE Products (product_id INT NOT NULL, name VARCHAR(100) NOT NULL);

25. UNIQUE Constraint: Ensuring Uniqueness

Ensures that all values in a column are unique.
Example:CREATE TABLE Employees (email VARCHAR(100) UNIQUE);

26. ALTER TABLE: Modifying a Table Structure

ALTER TABLEIt isUsed to modify an existing table.
Example:ALTER TABLE Employees ADD COLUMN salary INT;

27. DROP TABLE: Deleting a Table

Removes a table and all of its data.
Example:DROP TABLE Students;

28. UNION: Combining Results from Multiple Queries

Combines results from multiple SELECTstatements.
Example:SELECT name FROM Employees UNION SELECT name FROM Customers;

29. DISTINCT Keyword: Removing Duplicate Data

Used to return only distinct (unique) values.
Example:SELECT DISTINCT department FROM Employees;

30. LIMIT: Restricting Query Results

Limits the number of rows returned by a query.
Example:SELECT * FROM Employees LIMIT 5;

31. BETWEEN: Filtering Within a Range

Filters data within a certain range.
Example:SELECT * FROM Employees WHERE salary BETWEEN 30000 AND 60000;

32. LIKE: Pattern Matching

Used to search for a specified pattern.
Example:SELECT * FROM Employees WHERE name LIKE 'J%';

33. IN: Matching Multiple Values

Filters data by matching it against a list of values.
Example:SELECT * FROM Employees WHERE department IN ('HR', 'Sales');

34. IS NULL: Finding Null Values

Filters rows with NULL values.
Example:SELECT * FROM Employees WHERE manager_id IS NULL;

35. CASE Statement: Conditional Logic

Allows for conditional logic within a query.
Example:SELECT name, CASE WHEN salary > 50000 THEN 'High' ELSE 'Low' END AS salary_level FROM Employees;

36. Transactions: Ensuring Data Consistency

A transaction ensures that a series of operations are executed successfully or rolled back.
Example:BEGIN TRANSACTION; UPDATE Employees SET salary = 50000; COMMIT;

37. COMMIT and ROLLBACK

COMMITSaves changes; ROLLBACKundoes changes made during a transaction.

38. Views: Virtual Tables

A viewVIEWis a virtual table that stores a query result.
Example:CREATE VIEW EmployeeDetails AS SELECT name, department FROM Employees WHERE salary > 50000;

39. Indexes: Speeding Up Queries

An index improves query performance by allowing faster searching and sorting.
Example:CREATE INDEX idx_department ON Employees(department);

40. Normalization: Organizing Data Efficiently

Process of organizing data to reduce redundancy and dependency.
Levels: 1NF, 2NF, 3NF, etc.

41. Denormalization: Optimizing Query Performance

Denormalization involves combining tables for faster querying at the expense of data redundancy.

42. Temporary Tables: Storing Data Temporarily

Temporary tables store data only for the duration of the session.
Example:CREATE TEMPORARY TABLE temp_table AS SELECT * FROM Employees;

43. Common Table Expressions (CTEs): Simplifying Queries

CTEs improve readability and allow for easier reuse of subqueries.
Example:WITH DepartmentCTE AS (SELECT department, COUNT(*) FROM Employees GROUP BY department) SELECT * FROM DepartmentCTE;

44. Recursive Queries: Handling Hierarchical Data

Recursive queries are used to query hierarchical data like organizational charts.
Example:WITH RECURSIVE OrgChart AS (SELECT id, manager_id, name FROM Employees WHERE manager_id IS NULL UNION ALL SELECT e.id, e.manager_id, e.name FROM Employees e JOIN OrgChart o ON e.manager_id = o.id) SELECT * FROM OrgChart;

45. EXPLAIN: Query Optimization

EXPLAINProvides information about how SQL statements are executed.
Example:EXPLAIN SELECT * FROM Employees WHERE salary > 50000;

46. SQL Functions: Built-in Operations

SQL includes various built-in functions like NOW(), LENGTH(), CONCAT(), etc.

47. SQL Injection: Security Risks

SQL injection occurs when malicious code is inserted into SQL queries.
Prevent it by using parameterized queries or stored procedures.

48. Database Backups: Data Protection

Regular backups ensure data recovery in case of failure.

49. Roles and Permissions: Controlling Access

Use roles and permissions to control user access to different parts of a database.

50. Monitoring and Logging: Tracking Changes

SQL logs can help monitor database activity and troubleshoot issues.

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