以“MySQL必知必会”开头的文章大部分是学习**《MySQL必知必会》**这本之前没看完的经典书籍的学习记录。
主要内容：会按照书中目录step by step进行，使用navicat可视化软件，根据目录的需求驱动，记录SQL语句、分析与结果。当然，这部分知识并不是孤立的，有时会结合python进行实现，会参考《高性能MySQL》、《数据库系统概论》等资料关联重要原理，还会对一些可用的ORM API的实例化操作进行记录。
一，连接数据库
使用python连接MySQL数据库：
先创建数据库：
CREATE TABLE `users` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`email` varchar(255) COLLATE utf8_bin NOT NULL,
`password` varchar(255) COLLATE utf8_bin NOT NULL,
PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 COLLATE=utf8_bin
AUTO_INCREMENT=1 ;
连接并操作：
import pymysql.cursors
# Connect to the database
connection = pymysql.connect(host='localhost',
user='root',
password='root',
db='test',
port=3306,
charset="utf8",
cursorclass=pymysql.cursors.DictCursor)
try:
with connection.cursor() as cursor:
# Create a new record
sql = "INSERT INTO `users` (`email`, `password`) VALUES (%s, %s)"
cursor.execute(sql, ('[email protected]', 'very-secret'))
# connection is not autocommit by default. So you must commit to save your changes.
connection.commit()
with connection.cursor() as cursor:
# Read a single record
sql = "SELECT `id`, `password` FROM `users` WHERE `email`=%s"
cursor.execute(sql, ('[email protected]',))
result = cursor.fetchone()
print(result)
finally:
connection.close()
打印：
{
'id': 1, 'password': 'very-secret'}
- 使用pymysql提供的参数化语句避免注入。
二，创建及使用数据库
1，创建数据库：
mysql> CREATE DATABASE crashcourse;
Query OK, 1 row affected (0.10 sec)
mysql> show create database crashcourse;
+-------------+---------------------------------------------------------------------------------------------------------------------------------------+
| Database | Create Database |
+-------------+---------------------------------------------------------------------------------------------------------------------------------------+
| crashcourse | CREATE DATABASE `crashcourse` /*!40100 DEFAULT CHARACTER SET utf8mb4 COLLATE utf8mb4_0900_ai_ci */ /*!80016 DEFAULT ENCRYPTION='N' */ |
+-------------+---------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.02 sec)
mysql> show databases; # 了解数据库，返回数据库列表
+--------------------+
| Database |
+--------------------+
| crashcourse |
| information_schema |
| messageboard |
| mysql |
| mysqlite3 |
| performance_schema |
| spyders |
| sys |
+--------------------+
8 rows in set (0.01 sec)
2，使用数据库：
mysql> use crashcourse; #指定使用的数据库
Database changed
三，创建及使用数据表
1，创建数据表：
CREATE TABLE customers
(
cust_id int NOT NULL AUTO_INCREMENT,
cust_name char(50) NOT NULL ,
cust_address char(50) NULL ,
cust_city char(50) NULL ,
cust_state char(5) NULL ,
cust_zip char(10) NULL ,
cust_country char(50) NULL ,
cust_contact char(50) NULL ,
cust_email char(255) NULL ,
PRIMARY KEY (cust_id)
) ENGINE=InnoDB;
mysql> sshow create table productnotes; #查看创建表productnotes表的mysql代码语句
+--------------+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Table | Create Table |
+--------------+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| productnotes | CREATE TABLE `productnotes` (
`note_id` int NOT NULL AUTO_INCREMENT,
`prod_id` char(10) NOT NULL,
`note_date` datetime NOT NULL,
`note_text` text,
PRIMARY KEY (`note_id`),
FULLTEXT KEY `note_text` (`note_text`)
) ENGINE=MyISAM DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_0900_ai_ci |
+--------------+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.03 sec)
mysql> show tables;
+-----------------------+
| Tables_in_crashcourse |
+-----------------------+
| customers |
| orderitems |
| orders |
| productnotes |
| products |
| vendors |
+-----------------------+
6 rows in set (0.01 sec)
2，使用数据表：
插入数据：
INSERT INTO customers(cust_id, cust_name, cust_address, cust_city, cust_state, cust_zip, cust_country, cust_contact, cust_email)
VALUES(10001, 'Coyote Inc.', '200 Maple Lane', 'Detroit', 'MI', '44444', 'USA', 'Y Lee', '[email protected]');
INSERT INTO customers(cust_id, cust_name, cust_address, cust_city, cust_state, cust_zip, cust_country, cust_contact)
VALUES(10002, 'Mouse House', '333 Fromage Lane', 'Columbus', 'OH', '43333', 'USA', 'Jerry Mouse');
INSERT INTO customers(cust_id, cust_name, cust_address, cust_city, cust_state, cust_zip, cust_country, cust_contact, cust_email)
VALUES(10003, 'Wascals', '1 Sunny Place', 'Muncie', 'IN', '42222', 'USA', 'Jim Jones', '[email protected]');
INSERT INTO customers(cust_id, cust_name, cust_address, cust_city, cust_state, cust_zip, cust_country, cust_contact, cust_email)
VALUES(10004, 'Yosemite Place', '829 Riverside Drive', 'Phoenix', 'AZ', '88888', 'USA', 'Y Sam', '[email protected]');
INSERT INTO customers(cust_id, cust_name, cust_address, cust_city, cust_state, cust_zip, cust_country, cust_contact)
VALUES(10005, 'E Fudd', '4545 53rd Street', 'Chicago', 'IL', '54545', 'USA', 'E Fudd');
显示表列：
mysql> show columns from customers;
+--------------+-----------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+--------------+-----------+------+-----+---------+----------------+
| cust_id | int | NO | PRI | NULL | auto_increment |
| cust_name | char(50) | NO | | NULL | |
| cust_address | char(50) | YES | | NULL | |
| cust_city | char(50) | YES | | NULL | |
| cust_state | char(5) | YES | | NULL | |
| cust_zip | char(10) | YES | | NULL | |
| cust_country | char(50) | YES | | NULL | |
| cust_contact | char(50) | YES | | NULL | |
| cust_email | char(255) | YES | | NULL | |
+--------------+-----------+------+-----+---------+----------------+
9 rows in set (0.02 sec)
3，使用SHOW查看一些内部信息：
show status; # 用于显示广泛的服务器状态信息
show grants; #显示授予用户（所有用户或特定用户）的安全权限
show errors; # 显示服务器错误内容
show warnings； #显示服务器警告内容
四，使用SELECT检索数据
SELECT的用途是从一个或多个表中检索信息。
1，检索单个列
使用SELECT，必须至少给出——想选择什么，以及从什么地方选择。
mysql> select prod_name from products; # 从products表中检索prod_name 单列
+----------------+
| prod_name |
+----------------+
| .5 ton anvil |
| 1 ton anvil |
| 2 ton anvil |
| Detonator |
| Bird seed |
| Carrots |
| Fuses |
| JetPack 1000 |
| JetPack 2000 |
| Oil can |
| Safe |
| Sling |
| TNT (1 stick) |
| TNT (5 sticks) |
+----------------+
14 rows in set (0.03 sec)
- 如果没有明确排序查询结果（下一章介绍），则返回的数据的顺序没有特殊意义。
2，检索多个列
在SELECT关键字后给出多个列名，列名之间必须以逗号分隔。
mysql> select prod_id,prod_name,prod_price from products; # 从products表中检索prod_name，prod_name,prod_price 多列
+---------+----------------+------------+
| prod_id | prod_name | prod_price |
+---------+----------------+------------+
| ANV01 | .5 ton anvil | 5.99 |
| ANV02 | 1 ton anvil | 9.99 |
| ANV03 | 2 ton anvil | 14.99 |
| DTNTR | Detonator | 13.00 |
| FB | Bird seed | 10.00 |
| FC | Carrots | 2.50 |
| FU1 | Fuses | 3.42 |
| JP1000 | JetPack 1000 | 35.00 |
| JP2000 | JetPack 2000 | 55.00 |
| OL1 | Oil can | 8.99 |
| SAFE | Safe | 50.00 |
| SLING | Sling | 4.49 |
| TNT1 | TNT (1 stick) | 2.50 |
| TNT2 | TNT (5 sticks) | 10.00 |
+---------+----------------+------------+
14 rows in set (0.03 sec)
- 从上述输出可以看到， SQL语句一般返回原始的、无格式的数据。数据的格式化是一个表示问题，而不是一个检索问题。
3，检索所有列
在实际列名的位置使用星号（*）通配符。
mysql> select * from products; # 从products表中检索所有列，通常情况下，检索不需要的列会降低检索和应用程序的效率
+---------+---------+----------------+------------+----------------------------------------------------------------+
| prod_id | vend_id | prod_name | prod_price | prod_desc |
+---------+---------+----------------+------------+----------------------------------------------------------------+
| ANV01 | 1001 | .5 ton anvil | 5.99 | .5 ton anvil, black, complete with handy hook |
| ANV02 | 1001 | 1 ton anvil | 9.99 | 1 ton anvil, black, complete with handy hook and carrying case |
| ANV03 | 1001 | 2 ton anvil | 14.99 | 2 ton anvil, black, complete with handy hook and carrying case |
| DTNTR | 1003 | Detonator | 13.00 | Detonator (plunger powered), fuses not included |
| FB | 1003 | Bird seed | 10.00 | Large bag (suitable for road runners) |
| FC | 1003 | Carrots | 2.50 | Carrots (rabbit hunting season only) |
| FU1 | 1002 | Fuses | 3.42 | 1 dozen, extra long |
| JP1000 | 1005 | JetPack 1000 | 35.00 | JetPack 1000, intended for single use |
| JP2000 | 1005 | JetPack 2000 | 55.00 | JetPack 2000, multi-use |
| OL1 | 1002 | Oil can | 8.99 | Oil can, red |
| SAFE | 1003 | Safe | 50.00 | Safe with combination lock |
| SLING | 1003 | Sling | 4.49 | Sling, one size fits all |
| TNT1 | 1003 | TNT (1 stick) | 2.50 | TNT, red, single stick |
| TNT2 | 1003 | TNT (5 sticks) | 10.00 | TNT, red, pack of 10 sticks |
+---------+---------+----------------+------------+----------------------------------------------------------------+
14 rows in set (0.03 sec)
4，检索不同的行
使用DISTINCT关键字，此关键字指示MySQL只返回不同的值。
mysql> select prod_id,vend_id from products;
+---------+---------+
| prod_id | vend_id |
+---------+---------+
| ANV01 | 1001 |
| ANV02 | 1001 |
| ANV03 | 1001 |
| FU1 | 1002 |
| OL1 | 1002 |
| DTNTR | 1003 |
| FB | 1003 |
| FC | 1003 |
| SAFE | 1003 |
| SLING | 1003 |
| TNT1 | 1003 |
| TNT2 | 1003 |
| JP1000 | 1005 |
| JP2000 | 1005 |
+---------+---------+
14 rows in set (0.03 sec)
mysql> select distinct vend_id from products;
+---------+
| vend_id |
+---------+
| 1001 |
| 1002 |
| 1003 |
| 1005 |
+---------+
4 rows in set (0.03 sec)
- DISTINCT关键字应用于所有列而不仅是前置它的列。如果给出SELECT DISTINCT vend_id,prod_price，除非指定的两个列都不同，否则所有行都将被检索出来.
5，结果限制
1，返回第一行或前几行，可使用LIMIT子句：
mysql> select prod_name from products limit 5; #从第 0 行开始，返回前 5 行
+--------------+
| prod_name |
+--------------+
| .5 ton anvil |
| 1 ton anvil |
| 2 ton anvil |
| Detonator |
| Bird seed |
+--------------+
5 rows in set (0.03 sec)
- 带一个值的
LIMIT总是从第一行开始，给出的数为返回的行数。
2，返回从行5开始的5行：
mysql> select prod_name from products limit 5,5;#从第 5 行开始，检索 5 行
+--------------+
| prod_name |
+--------------+
| Carrots |
| Fuses |
| JetPack 1000 |
| JetPack 2000 |
| Oil can |
+--------------+
5 rows in set (0.03 sec)
- 带两个值的LIMIT可以指定从行号为第一个值的位置开始。
mysql> select prod_name from products limit 4 OFFSET 3; #从第 3 行开始，检索 4 行
+-----------+
| prod_name |
+-----------+
| Detonator |
| Bird seed |
| Carrots |
| Fuses |
+-----------+
4 rows in set (0.03 sec)
- 这是MySQL 5支持LIMIT的另一种替代语法
6，使用完全限定的表名
使用完全限定的名字来引用列（同时使用表名和列字）。
select products.prod_name from products;
等价于
select prod_name from products;
等价于
select products.prod_name from crashcourse.products;
五，排序数据
使用SELECT语句的ORDER BY子句，ORDER BY子句取一个或多个列的名字，根据需要排序检索出的数据。
- SQL语句由子句构成，有些子句是必需的，而有的是可选的。一个子句通常由一个关键字和所提供的数据组成。
mysql> select prod_name from products order by prod_name;
+----------------+
| prod_name |
+----------------+
| .5 ton anvil |
| 1 ton anvil |
| 2 ton anvil |
| Bird seed |
| Carrots |
| Detonator |
| Fuses |
| JetPack 1000 |
| JetPack 2000 |
| Oil can |
| Safe |
| Sling |
| TNT (1 stick) |
| TNT (5 sticks) |
+----------------+
14 rows in set (0.03 sec)
- 通常， ORDER BY子句中使用的列将是为显示所选择的列。但是，实际上并不一定要这样，用非检索的列排序数据是完全合法的。
六，按多个列排序
只要指定列名，列名之间用逗号分开即可。
mysql> select prod_id, prod_price,prod_name from products order by prod_price, prod_name; #先按价格，再按产品名排序
+---------+------------+----------------+
| prod_id | prod_price | prod_name |
+---------+------------+----------------+
| FC | 2.50 | Carrots |
| TNT1 | 2.50 | TNT (1 stick) |
| FU1 | 3.42 | Fuses |
| SLING | 4.49 | Sling |
| ANV01 | 5.99 | .5 ton anvil |
| OL1 | 8.99 | Oil can |
| ANV02 | 9.99 | 1 ton anvil |
| FB | 10.00 | Bird seed |
| TNT2 | 10.00 | TNT (5 sticks) |
| DTNTR | 13.00 | Detonator |
| ANV03 | 14.99 | 2 ton anvil |
| JP1000 | 35.00 | JetPack 1000 |
| SAFE | 50.00 | Safe |
| JP2000 | 55.00 | JetPack 2000 |
+---------+------------+----------------+
14 rows in set (0.03 sec)
七，指定排序方向
1，降序排列desc：
mysql> select prod_id, prod_price,prod_name from products order by prod_price desc, prod_name; #先按价格降序排列，再按产品名升序排列
+---------+------------+----------------+
| prod_id | prod_price | prod_name |
+---------+------------+----------------+
| JP2000 | 55.00 | JetPack 2000 |
| SAFE | 50.00 | Safe |
| JP1000 | 35.00 | JetPack 1000 |
| ANV03 | 14.99 | 2 ton anvil |
| DTNTR | 13.00 | Detonator |
| FB | 10.00 | Bird seed |
| TNT2 | 10.00 | TNT (5 sticks) |
| ANV02 | 9.99 | 1 ton anvil |
| OL1 | 8.99 | Oil can |
| ANV01 | 5.99 | .5 ton anvil |
| SLING | 4.49 | Sling |
| FU1 | 3.42 | Fuses |
| FC | 2.50 | Carrots |
| TNT1 | 2.50 | TNT (1 stick) |
+---------+------------+----------------+
14 rows in set (0.03 sec)
- 若包含desc，则使用的降序，未用的默认为升序ASC
指定具体列的升降序
mysql> select prod_id, prod_price,prod_name from products order by prod_price desc, prod_name desc; #先按价格降序排列，再按产品名降序排列
+---------+------------+----------------+
| prod_id | prod_price | prod_name |
+---------+------------+----------------+
| JP2000 | 55.00 | JetPack 2000 |
| SAFE | 50.00 | Safe |
| JP1000 | 35.00 | JetPack 1000 |
| ANV03 | 14.99 | 2 ton anvil |
| DTNTR | 13.00 | Detonator |
| TNT2 | 10.00 | TNT (5 sticks) |
| FB | 10.00 | Bird seed |
| ANV02 | 9.99 | 1 ton anvil |
| OL1 | 8.99 | Oil can |
| ANV01 | 5.99 | .5 ton anvil |
| SLING | 4.49 | Sling |
| FU1 | 3.42 | Fuses |
| TNT1 | 2.50 | TNT (1 stick) |
| FC | 2.50 | Carrots |
+---------+------------+----------------+
14 rows in set (0.03 sec)
- 在字典（ dictionary）排序顺序中，A被视为与a相同，这是MySQL（和大多数数据库管理系统）的默认行为。但是，许多数据库管理员能够在需要时改变这种行为（如果你的数据库包含大量外语字符，可能必须这样做）。
八，简单应用
使用ORDER BY和LIMIT的组合，能够找出一个列中最高或最低的值。
mysql> select prod_price from products order by prod_price desc limit 1; # 最高值
+------------+
| prod_price |
+------------+
| 55.00 |
+------------+
1 row in set (0.13 sec)
mysql> select prod_price from products order by prod_price asc limit 1; # 最低值
+------------+
| prod_price |
+------------+
| 2.50 |
+------------+
1 row in set (0.03 sec)
- 先排序，在限制取值。