這是一份作業，僅此而已。
程式碼僅供參考。

# 建立資料庫yggl_mllt9920
CREATE DATABASE yggl_mllt9920;
# 選擇資料庫
USE yggl_mllt9920;
# 建立資料表 salary_mllt9920
CREATE TABLE salary_mllt9920(
員工編號 CHAR(6) NOT NULL PRIMARY KEY,
收入 Float(8,2) NOT NULL,
支出 Float(8,2) NOT NULL
);
# 建立資料表 departments_mllt9920
CREATE TABLE departments_mllt9920(
部門編號 CHAR(3) NOT NULL PRIMARY KEY,
部門名稱 CHAR(20) NOT NULL,
備註 TEXT(16) NOT NULL
);
# 查詢所有資料表
SHOW TABLES;
DESC salary_mllt9920;
DESC departments_mllt9920;

# 複製資料表departments_mllt9920_test
CREATE TABLE departments_mllt9920_test LIKE departments_mllt9920;
DESC departments_mllt9920_test;

# 在表中新建列
ALTER TABLE departments_mllt9920_test
ADD COLUMN 電話 CHAR(12) NOT NULL;
DESC departments_mllt9920_test;

# 修改預設值
ALTER TABLE departments_mllt9920_test MODIFY  電話 CHAR(12) NOT NULL DEFAULT '010123456789';
DESC departments_mllt9920_test;

# 修改欄位名
ALTER TABLE departments_mllt9920_test CHANGE 電話 部門電話 CHAR(12);
DESC departments_mllt9920_test;

# 修改欄位型別
ALTER TABLE departments_mllt9920_test MODIFY  部門電話 VARCHAR(18) NOT NULL DEFAULT '010123456789';
DESC departments_mllt9920_test;

# 刪除欄位
ALTER TABLE departments_mllt9920_test DROP COLUMN 備註;
DESC departments_mllt9920_test;

# 修改欄位名-方法2
ALTER TABLE departments_mllt9920_test RENAME COLUMN 部門電話 TO 部門主管電話;
DESC departments_mllt9920_test;