Day 2:SQL

Source: Dev.to

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

String / Character Data Types

Date & Time Data Types

3. CREATE TABLE with Data Types

CREATE TABLE employees (
    emp_id    INT,
    emp_name  VARCHAR(50),
    salary    DECIMAL(10,2),
    join_date DATE
);

4. Viewing Table Structure

• Describe a table

DESCRIBE employees;

• Show all tables

SHOW TABLES;

5. INSERT Data (Detailed)

• Insert a 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

• Use meaningful names.
• Avoid SQL keywords.
• Prefer lowercase with underscores.

Correct: employee_details
Incorrect: select, table