Day 2:SQL

#sql #tutorial #database #beginners

Database Structure, Data Types & Table Basics

1. Database Structure Recap
A Relational Database contains:

Database
Tables
Rows (Records)
Columns (Fields) Example: Database → school Table → students Columns → student_id, name, age, city

2. SQL Data Types (VERY IMPORTANT)

Numeric Data Types
| Data Type | Description | Example |
| ------------ | --------------- | ------- |
| INT | Whole numbers | 10, 25 |
| BIGINT | Large integers | 1000000 |
| DECIMAL(p,s) | Decimal numbers | 99.50 |

String / Character Data Types
| Data Type | Description | Example |
| ---------- | -------------------- | ------- |
| CHAR(n) | Fixed-length text | 'A' |
| VARCHAR(n) | Variable-length text | 'Aruna' |
| TEXT | Large text | Address |

Date & Time Data Types
| Data Type | Description | Example |
| --------- | ----------- | ------------------- |
| DATE | YYYY-MM-DD | 2025-01-10 |
| TIME | HH:MM:SS | 10:30:00 |
| DATETIME | Date + Time | 2025-01-10 10:30:00 |

3. CREATE TABLE with Data Types
Defines table structure clearly.
CREATE TABLE employees (
emp_id INT,
emp_name VARCHAR(50),
salary DECIMAL(10,2),
join_date DATE
);

4. Viewing Table Structure
DESCRIBE table
DESCRIBE employees;
SHOW TABLES
SHOW TABLES;

5. INSERT Data (Detailed)
Insert single row:
INSERT INTO employees
(emp_id, emp_name, salary, join_date)
VALUES (101, 'Ravi', 35000.50, '2024-06-15');
Insert multiple rows:
INSERT INTO employees VALUES
(102, 'Priya', 42000.00, '2024-07-01'),
(103, 'Karthik', 38000.75, '2024-08-10');

6. SELECT Basics (More Detail)
Select all columns:
SELECT * FROM employees;
Select specific columns:
SELECT emp_name, salary FROM employees;

7. Table Naming Rules