Chapter 2SQL Tutorial~1 min read
CREATE TABLE & Data Types
Table बनवणे — Structure Define करणे
Table बनवायला CREATE TABLE statement वापरतात. प्रत्येक column ला name आणि data type द्यायला लागतो. Constraints (NOT NULL, UNIQUE, PRIMARY KEY) data integrity ensure करतात.
Common Data Types
- ▸INT / BIGINT — whole numbers (age, marks, count)
- ▸DECIMAL(p,s) / FLOAT — decimal numbers (price = DECIMAL(10,2))
- ▸VARCHAR(n) — variable-length string, max n chars
- ▸CHAR(n) — fixed-length string (phone numbers, codes)
- ▸TEXT — long text (descriptions, content)
- ▸DATE — YYYY-MM-DD (2024-01-15)
- ▸DATETIME / TIMESTAMP — date + time
- ▸BOOLEAN / TINYINT(1) — true/false
CREATE TABLE with constraints
sql
CREATE DATABASE school;
USE school;
-- Students table
CREATE TABLE students (
id INT PRIMARY KEY AUTO_INCREMENT, -- unique, auto-increment
name VARCHAR(100) NOT NULL, -- NULL नाही चालत
email VARCHAR(150) UNIQUE, -- duplicate नाही
city VARCHAR(50) DEFAULT 'Pune', -- default value
marks INT CHECK (marks >= 0 AND marks <= 100),
dob DATE,
created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP
);
-- Courses table
CREATE TABLE courses (
id INT PRIMARY KEY AUTO_INCREMENT,
title VARCHAR(200) NOT NULL,
duration INT NOT NULL, -- in hours
fee DECIMAL(8,2) DEFAULT 0.00
);INSERT INTO — Data Add करणे
Single and multiple row insert
sql
-- Single row insert
INSERT INTO students (name, email, city, marks)
VALUES ('Rahul Patil', 'rahul@gmail.com', 'Pune', 85);
-- Multiple rows एकाच वेळी
INSERT INTO students (name, email, city, marks)
VALUES
('Priya Desai', 'priya@gmail.com', 'Mumbai', 92),
('Amit Shinde', 'amit@gmail.com', 'Nagpur', 78),
('Sneha Kulkarni','sneha@gmail.com', 'Pune', 88),
('Ravi Jadhav', 'ravi@gmail.com', 'Nashik', 45),
('Kavita More', NULL, 'Mumbai', 35);
-- Columns skip केले (default/NULL येतो)
INSERT INTO students (name, marks)
VALUES ('Test User', 70);ALTER TABLE — Structure बदलणे
ALTER TABLE examples
sql
-- नवा column add करणे
ALTER TABLE students ADD phone VARCHAR(15);
-- Column modify करणे
ALTER TABLE students MODIFY COLUMN city VARCHAR(100);
-- Column rename करणे (MySQL 8+)
ALTER TABLE students RENAME COLUMN phone TO mobile;
-- Column delete करणे
ALTER TABLE students DROP COLUMN mobile;
-- Table rename करणे
RENAME TABLE students TO learners;
RENAME TABLE learners TO students; -- back✅ Key Points — लक्षात ठेवा
- ▸PRIMARY KEY — unique row identifier, NOT NULL + UNIQUE
- ▸AUTO_INCREMENT — automatically 1,2,3... generate
- ▸NOT NULL — empty value नाही चालत
- ▸UNIQUE — duplicate values नाही
- ▸DEFAULT value — column blank असेल तर हे येते
- ▸CHECK (condition) — value valid आहे का validate
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