建立一個數據庫

CREATE DATABASE IF NOT EXISTS sql_example

刪除一個數據庫

DROP DATABASE IF EXISTS sql_example

建立資料表

USE sql_example;
DROP TABLE IF EXISTS customers;

CREATE TABLE customers (
  customer_id INT PRIMARY KEY AUTO INCREMENT,
  first_name VARCHAR(50) NOT NULL
)

修改資料表

ALTER TABLE customers
  ADD city VARCHAR(50) NOT NULL AFTER first_name,
  MODIFY first_name VARCHAR(45) NOT NULL,
  DROP email;
 

刪除資料表

DROP TABLE IF EXISTS customers;

建立關係

DROP TABLE IF EXISTS orders;
DROP TABLE IF EXISTS customers;

CREATE TABLE customers (
	customer_id INT PRIMARY KEY AUTO_INCREMENT,
  	first_name VARCHAR(50) NOT NULL,
  	last_name VARCHAR(50) NOT NULL,
);

CREATE TABLE orders (
	customer_id INT NOT NULL,
  	order_id INT PRIMARY KEY,
  	FOREIGN KEY fk_orders_customers(customer_id)
  	REFERENCES customers (customer_id)
  	ON UPDATE CASCADE
  	ON DELETE NO ACTION
)
 

說明：FOREIGN KEY 外來鍵名字 (新增外來鍵的列)， REFERENCES 關聯的表 (關聯的欄位) ON UPDATE 操作 ON DELETE 操作