MySQL 是一種關系型數據庫管理系統，因其簡單易用和高效性受到廣泛的應用。下面介紹一些 MySQL 常見的命令和語法：

1. 連接數據庫
$ mysql -u username -p 密碼
2. 創建數據庫
CREATE DATABASE databasename;
3. 選擇數據庫
USE databasename;
4. 創建表格
CREATE TABLE tablename (
field1 datatype constraint,
field2 datatype constraint,
…
);
5. 查看表格
DESCRIBE tablename;
6. 插入數據
INSERT INTO tablename (field1, field2, …)
VALUES (value1, value2, …);
7. 更新數據
UPDATE tablename
SET field1=value1, field2=value2, …
WHERE condition;
8. 刪除數據
DELETE FROM tablename
WHERE condition;
9. 選擇數據
SELECT field1, field2, …
FROM tablename
WHERE condition
GROUP BY field
HAVING condition
ORDER BY field ASC/DESC;
10. 清空表格
TRUNCATE tablename;
11. 刪除表格
DROP TABLE tablename;
12. 連接表格
SELECT *
FROM tab1
INNER JOIN tab2
ON tab1.col1 = tab2.col2;
13. 創建索引
CREATE INDEX indexname
ON tablename (columnname);
14. 刪除索引
DROP INDEX indexname ON tablename;