关系数据库标准语言SQL01
结构化查询语言（Structured Query Language）简称SQL，是一种特殊目的的编程语言，是一种数据库查询和程序设计语言，用于存取数据以及查询、更新和管理关系数据库系统。
结构化查询语言是高级的非过程化编程语言，允许用户在高层数据结构上工作。它不要求用户指定对数据的存放方法，也不需要用户了解具体的数据存放方式，所以具有完全不同底层结构的不同数据库系统, 可以使用相同的结构化查询语言作为数据输入与管理的接口。结构化查询语言语句可以嵌套，这使它具有极大的灵活性和强大的功能。
关系数据库标准语言SQL02
文章目录
- SQL语言介绍
-
- SQL的特点
- SQL语言的组成
-
- 1.数据定义语言(DDL)
- 2.数据操纵语言(DML)
- 3.数据控制语言(DCL)
- 数据定义
-
- 数据库的定义和删除
-
- 1.创建数据库
- 2.选择数据库
- 3.删除数据库
- 数据类型
-
- 1.字符串类型
- 2.数值类型
- 3.日期和时间类型
- 4.布尔类型
- 基本表的定义、删除和修改
-
- 1.创建表
- 2.利用子查询来创建表
- 3.修改表的结构
- 4.截断表和删除表
- 数据查询
-
- 基本查询
-
- 查询所有列
- 查询指定的列
- 去掉重复行
- 为列起别名
- 比较判断
- 之间判断
- 字符串的模糊查询
- 空值判断
- 之内判断
- 排序
- 分组查询
-
- 聚合函数
- 按单列分组
- 按多列分组
- 使用HAVING子句
- 连接查询
-
- 相等连接
- 自身连接
- 左外连接
- 右外连接
- 子查询
-
- 返回单值的子查询
- 返回多值的子查询
- 合并查询结果
SQL语言介绍
SQL的特点
1.综合统一
2.高度非过程化
3.面向集合的操作方式
4.同一种语法结构提供两种使用方式
5.语言简洁、易学易用
SQL语言的组成
1.数据定义语言(DDL)
DDL用来定义、修改、删除数据库中的各种对象，包括创建、修改、删除或重命名模式对象(CREATE、ALTER、DROP、RENAME)的语句，以及删除表中所有行但不删除表(TRUNCATE)的语句等
2.数据操纵语言(DML)
DML的命令用来查询、插入、修改、删除数据库中的数据，包含用于查询数据(SELECT)、添加新行数据(INSERT)、修改现有行数据(UPDATE)、删除现有行数据(DELETE)的语句等
3.数据控制语言(DCL)
DCL用于事务控制、并发控制、完整性和安全性控制等。事务控制用于把一组DML语句组合起来形成一个事务并进行事务控制。通过事务语句可以把对数据所做的修改保存起来(COMMIT)或者回滚这些修改(ROLLBACK)。在事务中设置一个保存点(SAVEPOINT)，以便用于可能出现的回溯操作；通过管理权限(GRANT、REVOKE)等语句完成安全性控制以及通过锁定一个数据库表(LOCKTABLE)限制用户对数据访问等操作，实现并发控制。
数据定义
数据库的定义和删除
1.创建数据库
mysql> CREATE DATABASE LearnMySQL;
Query OK, 1 row affected (0.18 sec)
2.选择数据库
mysql> USE LearnMySQL;
Database changed
3.删除数据库
mysql> DROP DATABASE LearnMySQL;
Query OK, 0 rows affected (0.19 sec)
数据类型
1.字符串类型
CHAR:描述定长的字符串，说明格式为CHAR(L)，其中L为字符串长度，取值范围为1~255。比L大的值将被截断，比L小的值将用空格填补。
VARCHAR:描述变长的字符串，说明格式为VARCHAR(L)，其中L为字符串长度，取值范围为1~255。比L大的值将被截断，比L小的值不会用空格填补，按实际长度存储。
2.数值类型
INT:用于表示整数，存储长度默认为4个字节。
DECIMAL:可以用来表示所有的数值数据，说明格式为DECIMAL(p,s)，其中p表示数值数据的最大长度，s表示数值数据中小数点后的数字位数，p,s在定义时可以省略，例如DECIMAL(5)、DECIMAL
3.日期和时间类型
DATE:用来保存固定长度的日期数据
TIME:用来保存固定长度的时间数据
DATETIME:用来保存固定长度的日期时间数据。日期格式为’YYYY-MM-DD’；时间格式为’HH:MM:SS’；日期时间格式为’YYYY-MM-DD HH:MM:SS’。
4.布尔类型
BOOLEAN:TRUE、FALSE
基本表的定义、删除和修改
1.创建表
mysql> CREATE TABLE product
-> (
-> p_code DECIMAL(6),
-> p_name VARCHAR(30),
-> p_price DECIMAL(5,2)
-> );
Query OK, 0 rows affected (0.41 sec)
mysql> DESC product;
+---------+--------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+---------+--------------+------+-----+---------+-------+
| p_code | decimal(6,0) | YES | | NULL | |
| p_name | varchar(30) | YES | | NULL | |
| p_price | decimal(5,2) | YES | | NULL | |
+---------+--------------+------+-----+---------+-------+
3 rows in set (0.01 sec)
mysql> CREATE TABLE ord
-> (
-> id INT AUTO_INCREMENT PRIMARY KEY,
-> ordno DECIMAL(8),
-> p_code DECIMAL(6),
-> s_code DECIMAL(6),
-> ordate DATETIME DEFAULT CURRENT_TIMESTAMP,
-> price DECIMAL(8,2)
-> );
Query OK, 0 rows affected (0.34 sec)
将id列设置为自增类型字段
在默认情况下，自增类型字段的值从1开始，步长为1.
设置自增类型的字段，需将其设置为主键，否则数据表将创建失败。
同时，为ordate字段设置默认值为当前系统时间。
mysql> DESC ord;
+--------+--------------+------+-----+-------------------+-------------------+
| Field | Type | Null | Key | Default | Extra |
+--------+--------------+------+-----+-------------------+-------------------+
| id | int | NO | PRI | NULL | auto_increment |
| ordno | decimal(8,0) | YES | | NULL | |
| p_code | decimal(6,0) | YES | | NULL | |
| s_code | decimal(6,0) | YES | | NULL | |
| ordate | datetime | YES | | CURRENT_TIMESTAMP | DEFAULT_GENERATED |
| price | decimal(8,2) | YES | | NULL | |
+--------+--------------+------+-----+-------------------+-------------------+
6 rows in set (0.00 sec)
2.利用子查询来创建表
mysql> CREATE TABLE ord_c
-> SELECT * FROM ord;
Query OK, 0 rows affected (0.54 sec)
Records: 0 Duplicates: 0 Warnings: 0
3.修改表的结构
为表增加一个新列
mysql> ALTER TABLE ord_c
-> ADD telephone VARCHAR(11);
Query OK, 0 rows affected (0.27 sec)
Records: 0 Duplicates: 0 Warnings: 0
mysql> DESC ord_c;
+-----------+--------------+------+-----+-------------------+-------------------+
| Field | Type | Null | Key | Default | Extra |
+-----------+--------------+------+-----+-------------------+-------------------+
| id | int | NO | | 0 | |
| ordno | decimal(8,0) | YES | | NULL | |
| p_code | decimal(6,0) | YES | | NULL | |
| s_code | decimal(6,0) | YES | | NULL | |
| ordate | datetime | YES | | CURRENT_TIMESTAMP | DEFAULT_GENERATED |
| price | decimal(8,2) | YES | | NULL | |
| telephone | varchar(11) | YES | | NULL | |
+-----------+--------------+------+-----+-------------------+-------------------+
7 rows in set (0.00 sec)
修改一个表中已有的列
一个ALTER TABLE …MODIFY语句只能为表修改一列。
mysql> ALTER TABLE ord_c
-> MODIFY telephone VARCHAR(13) DEFAULT '0431-8657130';
Query OK, 0 rows affected (0.15 sec)
Records: 0 Duplicates: 0 Warnings: 0
mysql> DESC ord_c;
+-----------+--------------+------+-----+-------------------+-------------------+
| Field | Type | Null | Key | Default | Extra |
+-----------+--------------+------+-----+-------------------+-------------------+
| id | int | NO | | 0 | |
| ordno | decimal(8,0) | YES | | NULL | |
| p_code | decimal(6,0) | YES | | NULL | |
| s_code | decimal(6,0) | YES | | NULL | |
| ordate | datetime | YES | | CURRENT_TIMESTAMP | DEFAULT_GENERATED |
| price | decimal(8,2) | YES | | NULL | |
| telephone | varchar(13) | YES | | 0431-8657130 | |
+-----------+--------------+------+-----+-------------------+-------------------+
7 rows in set (0.00 sec)
从一个表中删除一列
mysql> ALTER TABLE ord_c
-> DROP telephone;
Query OK, 0 rows affected (0.53 sec)
Records: 0 Duplicates: 0 Warnings: 0
mysql> DESC ord_c;
+--------+--------------+------+-----+-------------------+-------------------+
| Field | Type | Null | Key | Default | Extra |
+--------+--------------+------+-----+-------------------+-------------------+
| id | int | NO | | 0 | |
| ordno | decimal(8,0) | YES | | NULL | |
| p_code | decimal(6,0) | YES | | NULL | |
| s_code | decimal(6,0) | YES | | NULL | |
| ordate | datetime | YES | | CURRENT_TIMESTAMP | DEFAULT_GENERATED |
| price | decimal(8,2) | YES | | NULL | |
+--------+--------------+------+-----+-------------------+-------------------+
6 rows in set (0.00 sec)
4.截断表和删除表
截断表
删除了表中所有数据行，但表的结构依然保留
mysql> TRUNCATE TABLE ord_c;
Query OK, 0 rows affected (0.54 sec)
删除表
不仅删除表中的数据而且删除表的结构。
mysql> DROP TABLE ord_c;
Query OK, 0 rows affected (0.22 sec)
mysql> DESC ord_c;
ERROR 1146 (42S02): Table 'learnmysql.ord_c' doesn't exist
数据查询
基本查询
查询所有列
mysql> select * from products;
+---------+---------------------+------------+
| prod_id | prod_name | prod_price |
+---------+---------------------+------------+
| BNBG01 | Fish bean bag toy | 3.49 |
| BNBG02 | Bird bean bag toy | 3.49 |
| BNBG03 | Rabbit bean bag toy | 3.49 |
| BR01 | 8 inch teddy bear | 5.99 |
| BR02 | 12 inch teddy bear | 8.99 |
| BR03 | 18 inch teddy bear | 11.99 |
| RGAN01 | Raggedy Ann | 4.99 |
| RYL01 | King doll | 9.49 |
| RYL02 | Queen dool | 9.49 |
+---------+---------------------+------------+
9 rows in set (0.04 sec)
查询指定的列
mysql> select prod_name from products;
+---------------------+
| prod_name |
+---------------------+
| Fish bean bag toy |
| Bird bean bag toy |
| Rabbit bean bag toy |
| 8 inch teddy bear |
| 12 inch teddy bear |
| 18 inch teddy bear |
| Raggedy Ann |
| King doll |
| Queen dool |
+---------------------+
9 rows in set (0.00 sec)
去掉重复行
复制了一张products表，并加入了一行重复数据
mysql> SELECT * FROM products_c;
+---------+---------------------+------------+
| prod_id | prod_name | prod_price |
+---------+---------------------+------------+
| BNBG01 | Fish bean bag toy | 3.49 |
| BNBG02 | Bird bean bag toy | 3.49 |
| BNBG03 | Rabbit bean bag toy | 3.49 |
| BR01 | 8 inch teddy bear | 5.99 |
| BR02 | 12 inch teddy bear | 8.99 |
| BR03 | 18 inch teddy bear | 11.99 |
| RGAN01 | Raggedy Ann | 4.99 |
| RYL01 | King doll | 9.49 |
| RYL02 | Queen dool | 9.49 |
| RYL02 | Queen dool | 9.49 |
+---------+---------------------+------------+
10 rows in set (0.00 sec)
mysql> SELECT DISTINCT * FROM products_c;
+---------+---------------------+------------+
| prod_id | prod_name | prod_price |
+---------+---------------------+------------+
| BNBG01 | Fish bean bag toy | 3.49 |
| BNBG02 | Bird bean bag toy | 3.49 |
| BNBG03 | Rabbit bean bag toy | 3.49 |
| BR01 | 8 inch teddy bear | 5.99 |
| BR02 | 12 inch teddy bear | 8.99 |
| BR03 | 18 inch teddy bear | 11.99 |
| RGAN01 | Raggedy Ann | 4.99 |
| RYL01 | King doll | 9.49 |
| RYL02 | Queen dool | 9.49 |
+---------+---------------------+------------+
9 rows in set (0.00 sec)
为列起别名
mysql> SELECT prod_id AS 产品编号,prod_name AS 产品名称,prod_price AS 产品价格 FROM products;
+--------------+---------------------+--------------+
| 产品编号 | 产品名称 | 产品价格 |
+--------------+---------------------+--------------+
| BNBG01 | Fish bean bag toy | 3.49 |
| BNBG02 | Bird bean bag toy | 3.49 |
| BNBG03 | Rabbit bean bag toy | 3.49 |
| BR01 | 8 inch teddy bear | 5.99 |
| BR02 | 12 inch teddy bear | 8.99 |
| BR03 | 18 inch teddy bear | 11.99 |
| RGAN01 | Raggedy Ann | 4.99 |
| RYL01 | King doll | 9.49 |
| RYL02 | Queen dool | 9.49 |
+--------------+---------------------+--------------+
9 rows in set (0.00 sec)
比较判断
mysql> SELECT * FROM products WHERE prod_id='BR01';
+---------+-------------------+------------+
| prod_id | prod_name | prod_price |
+---------+-------------------+------------+
| BR01 | 8 inch teddy bear | 5.99 |
+---------+-------------------+------------+
1 row in set (0.00 sec)
mysql> SELECT * FROM products WHERE prod_price >5;
+---------+--------------------+------------+
| prod_id | prod_name | prod_price |
+---------+--------------------+------------+
| BR01 | 8 inch teddy bear | 5.99 |
| BR02 | 12 inch teddy bear | 8.99 |
| BR03 | 18 inch teddy bear | 11.99 |
| RYL01 | King doll | 9.49 |
| RYL02 | Queen dool | 9.49 |
+---------+--------------------+------------+
之间判断
mysql> SELECT * FROM products WHERE prod_price BETWEEN 5 AND 9;
+---------+--------------------+------------+
| prod_id | prod_name | prod_price |
+---------+--------------------+------------+
| BR01 | 8 inch teddy bear | 5.99 |
| BR02 | 12 inch teddy bear | 8.99 |
+---------+--------------------+------------+
2 rows in set (0.00 sec)
字符串的模糊查询
%用于表示0个或任意多个字符；_表示任意一个字符
mysql> SELECT * FROM products WHERE prod_id LIKE 'R%';
+---------+-------------+------------+
| prod_id | prod_name | prod_price |
+---------+-------------+------------+
| RGAN01 | Raggedy Ann | 4.99 |
| RYL01 | King doll | 9.49 |
| RYL02 | Queen dool | 9.49 |
+---------+-------------+------------+
3 rows in set (0.00 sec)
mysql> SELECT * FROM products WHERE prod_id LIKE '_G%';
+---------+-------------+------------+
| prod_id | prod_name | prod_price |
+---------+-------------+------------+
| RGAN01 | Raggedy Ann | 4.99 |
+---------+-------------+------------+
1 row in set (0.00 sec)
mysql> SELECT * FROM products WHERE prod_id NOT LIKE 'B%';
+---------+-------------+------------+
| prod_id | prod_name | prod_price |
+---------+-------------+------------+
| RGAN01 | Raggedy Ann | 4.99 |
| RYL01 | King doll | 9.49 |
| RYL02 | Queen dool | 9.49 |
+---------+-------------+------------+
3 rows in set (0.00 sec)
空值判断
mysql> select * from websites;
+----+----------+---------------------------+-------+---------+
| id | name | url | alexa | country |
+----+----------+---------------------------+-------+---------+
| 1 | Google | https://www.google.cm/ | 1 | USA |
| 2 | Taobao | https://www.taobao.com/ | 13 | CN |
| 3 | Xuexi | http://www.xxx.cn | 888 | xxx |
| 4 | Weibo | http://weibo.com/ | 20 | CN |
| 5 | Facebook | https://www.facebook.com/ | 1 | USA |
| 6 | NULL | NULL | 50 | NULL |
+----+----------+---------------------------+-------+---------+
6 rows in set (0.00 sec)
mysql> SELECT * FROM websites WHERE url IS NULL;
+----+------+------+-------+---------+
| id | name | url | alexa | country |
+----+------+------+-------+---------+
| 6 | NULL | NULL | 50 | NULL |
+----+------+------+-------+---------+
1 row in set (0.00 sec)
mysql> SELECT * FROM websites WHERE url IS NOT NULL;
+----+----------+---------------------------+-------+---------+
| id | name | url | alexa | country |
+----+----------+---------------------------+-------+---------+
| 1 | Google | https://www.google.cm/ | 1 | USA |
| 2 | Taobao | https://www.taobao.com/ | 13 | CN |
| 3 | Xuexi | http://www.xxx.cn | 888 | xxx |
| 4 | Weibo | http://weibo.com/ | 20 | CN |
| 5 | Facebook | https://www.facebook.com/ | 1 | USA |
+----+----------+---------------------------+-------+---------+
5 rows in set (0.00 sec)
之内判断
mysql> SELECT prod_name,prod_price FROM products WHERE prod_id IN ('BR01','BR02') and prod_price <8;
+-------------------+------------+
| prod_name | prod_price |
+-------------------+------------+
| 8 inch teddy bear | 5.99 |
+-------------------+------------+
1 row in set (0.00 sec)
排序
默认ASC升序，加DESC降序
mysql> SELECT * FROM products ORDER BY prod_price;
+---------+---------------------+------------+
| prod_id | prod_name | prod_price |
+---------+---------------------+------------+
| BNBG01 | Fish bean bag toy | 3.49 |
| BNBG02 | Bird bean bag toy | 3.49 |
| BNBG03 | Rabbit bean bag toy | 3.49 |
| RGAN01 | Raggedy Ann | 4.99 |
| BR01 | 8 inch teddy bear | 5.99 |
| BR02 | 12 inch teddy bear | 8.99 |
| RYL01 | King doll | 9.49 |
| RYL02 | Queen dool | 9.49 |
| BR03 | 18 inch teddy bear | 11.99 |
+---------+---------------------+------------+
9 rows in set (0.00 sec)
mysql> SELECT * FROM products ORDER BY prod_price DESC;
+---------+---------------------+------------+
| prod_id | prod_name | prod_price |
+---------+---------------------+------------+
| BR03 | 18 inch teddy bear | 11.99 |
| RYL01 | King doll | 9.49 |
| RYL02 | Queen dool | 9.49 |
| BR02 | 12 inch teddy bear | 8.99 |
| BR01 | 8 inch teddy bear | 5.99 |
| RGAN01 | Raggedy Ann | 4.99 |
| BNBG01 | Fish bean bag toy | 3.49 |
| BNBG02 | Bird bean bag toy | 3.49 |
| BNBG03 | Rabbit bean bag toy | 3.49 |
+---------+---------------------+------------+
9 rows in set (0.00 sec)
SELECT语句中包含多个子句时，ORDER BY必须是最后一个子句
可以使用列的别名、位置进行排序
mysql> SELECT prod_price AS 产品价格 FROM products ORDER BY 产品价格 DESC;
+--------------+
| 产品价格 |
+--------------+
| 11.99 |
| 9.49 |
| 9.49 |
| 8.99 |
| 5.99 |
| 4.99 |
| 3.49 |
| 3.49 |
| 3.49 |
+--------------+
9 rows in set (0.00 sec)
对产品名称降序，对产品价格升序
mysql> SELECT * FROM products ORDER BY prod_name DESC,prod_price;
+---------+---------------------+------------+
| prod_id | prod_name | prod_price |
+---------+---------------------+------------+
| RGAN01 | Raggedy Ann | 4.99 |
| BNBG03 | Rabbit bean bag toy | 3.49 |
| RYL02 | Queen dool | 9.49 |
| RYL01 | King doll | 9.49 |
| BNBG01 | Fish bean bag toy | 3.49 |
| BNBG02 | Bird bean bag toy | 3.49 |
| BR01 | 8 inch teddy bear | 5.99 |
| BR03 | 18 inch teddy bear | 11.99 |
| BR02 | 12 inch teddy bear | 8.99 |
+---------+---------------------+------------+
9 rows in set (0.00 sec)
分组查询
聚合函数
mysql> SELECT COUNT(*) AS 产品总数,SUM(prod_price) AS 产品价格总和,AVG(prod_price) AS 平均价格,MAX(prod_price) AS 最高价,MIN(prod_price) AS 最低 价 FROM products;
+--------------+--------------------+--------------+-----------+-----------+
| 产品总数 | 产品价格总和 | 平均价格 | 最高价 | 最低价 |
+--------------+--------------------+--------------+-----------+-----------+
| 9 | 61.41 | 6.823333 | 11.99 | 3.49 |
+--------------+--------------------+--------------+-----------+-----------+
1 row in set (0.00 sec)
聚合函数只能出现在所查询的列、ORDER BY、HAVING子句中，不能出现在WHERE、GROUP BY子句中。
按单列分组
我对products表如下修改
mysql> SELECT * FROM products;
+----+---------+---------------------+------------+
| id | prod_id | prod_name | prod_price |
+----+---------+---------------------+------------+
| 1 | BNBG01 | Fish bean bag toy | 3.49 |
| 2 | BNBG01 | Bird bean bag toy | 3.49 |
| 3 | BNBG01 | Rabbit bean bag toy | 3.49 |
| 4 | BR01 | 8 inch teddy bear | 5.99 |
| 5 | BR01 | 12 inch teddy bear | 8.99 |
| 6 | BR01 | 18 inch teddy bear | 11.99 |
| 7 | RGAN01 | Raggedy Ann | 4.99 |
| 8 | RYL01 | King doll | 9.49 |
| 9 | RYL01 | Queen dool | 9.49 |
+----+---------+---------------------+------------+
9 rows in set (0.00 sec)
按产品编号分组，按产品编号升序输出每组产品的平均价格，最高价格和最低价格
mysql> SELECT prod_id AS 产品编号,AVG(prod_price) AS 平均价格,MAX(prod_price) AS 最高价格,MIN(prod_price) AS 最低价格 FROM products GROUP BY prod_id ORDER BY prod_id;
+--------------+--------------+--------------+--------------+
| 产品编号 | 平均价格 | 最高价格 | 最低价格 |
+--------------+--------------+--------------+--------------+
| BNBG01 | 3.490000 | 3.49 | 3.49 |
| BR01 | 8.990000 | 11.99 | 5.99 |
| RGAN01 | 4.990000 | 4.99 | 4.99 |
| RYL01 | 9.490000 | 9.49 | 9.49 |
+--------------+--------------+--------------+--------------+
4 rows in set (0.00 sec)
按多列分组
按产品编号和产品价格进行分组
mysql> SELECT * FROM products GROUP BY prod_id,prod_price ORDER BY prod_id;
+----+---------+--------------------+------------+
| id | prod_id | prod_name | prod_price |
+----+---------+--------------------+------------+
| 1 | BNBG01 | Fish bean bag toy | 3.49 |
| 4 | BR01 | 8 inch teddy bear | 5.99 |
| 5 | BR01 | 12 inch teddy bear | 8.99 |
| 6 | BR01 | 18 inch teddy bear | 11.99 |
| 7 | RGAN01 | Raggedy Ann | 4.99 |
| 8 | RYL01 | King doll | 9.49 |
+----+---------+--------------------+------------+
6 rows in set (0.00 sec)
使用HAVING子句
按产品编号分组，按产品编号升序输出产品平均价格大于8的组和其平均价格
mysql> SELECT prod_id AS 产品编号,AVG(prod_price) AS 平均价格 FROM products WHERE prod_id IS NOT NULL GROUP BY prod_id HAVING AVG(prod_price)>8;
+--------------+--------------+
| 产品编号 | 平均价格 |
+--------------+--------------+
| BR01 | 8.990000 |
| RYL01 | 9.490000 |
+--------------+--------------+
2 rows in set (0.00 sec)
上述语句也可写成
mysql> SELECT prod_id AS 产品编号,AVG(prod_price) AS 平均价格 FROM products WHERE prod_id IS NOT NULL GROUP BY prod_id HAVING 平均价格>8;
连接查询
现在需要再创建一个表
产品生产者的信息表
mysql> SELECT * FROM producers;
+----+------+---------+------+
| id | name | prod_id | age |
+----+------+---------+------+
| 1 | jack | BNBG01 | 28 |
| 2 | tom | BR01 | 25 |
| 3 | lucy | RYL01 | 24 |
+----+------+---------+------+
3 rows in set (0.00 sec)
相等连接
mysql> SELECT p1.prod_id AS 产品编号,p1.prod_name AS 产品名称,p2.name AS 生产者,p1.prod_price AS 产品价格 FROM products p1,producers p2 WHERE p1.prod_id=p2.prod_id ORDER BY 产品编号;
+--------------+---------------------+-----------+--------------+
| 产品编号 | 产品名称 | 生产者 | 产品价格 |
+--------------+---------------------+-----------+--------------+
| BNBG01 | Fish bean bag toy | jack | 3.49 |
| BNBG01 | Bird bean bag toy | jack | 3.49 |
| BNBG01 | Rabbit bean bag toy | jack | 3.49 |
| BR01 | 8 inch teddy bear | tom | 5.99 |
| BR01 | 12 inch teddy bear | tom | 8.99 |
| BR01 | 18 inch teddy bear | tom | 11.99 |
| RYL01 | King doll | lucy | 9.49 |
| RYL01 | Queen dool | lucy | 9.49 |
+--------------+---------------------+-----------+--------------+
8 rows in set (0.00 sec)
可以发现产品编号为RGAN01的产品信息没有输出，因为producers表里没有与其对应的生产者。
上述语句也可写成
mysql> SELECT p1.prod_id AS 产品编号,p1.prod_name AS 产品名称,p2.name AS 生产者,p1.prod_price AS 产品价格 FROM products p1 INNER JOIN producers p2 ON p1.prod_id=p2.prod_id ORDER BY 产品编号;
自身连接
再建个表，empno(雇员编号)，mgr(管理员编号)
mysql> SELECT * FROM emp;
+-------+-------+------+
| empno | ename | mgr |
+-------+-------+------+
| 7369 | SMITH | 7902 |
| 7566 | JONES | 7839 |
| 7788 | SCOTT | 7566 |
| 7839 | KING | NULL |
| 7876 | ADAMS | 7788 |
| 7902 | FORD | 7566 |
+-------+-------+------+
6 rows in set (0.00 sec)
把一个表映射成两个表，一个做雇员表，一个做管理员表，再把两个表连接起来
mysql> SELECT e.ename 雇员,m.ename 管理员 FROM emp e,emp m WHERE m.empno=e.mgr;
+--------+-----------+
| 雇员 | 管理员 |
+--------+-----------+
| SMITH | FORD |
| JONES | KING |
| SCOTT | JONES |
| ADAMS | SCOTT |
| FORD | JONES |
+--------+-----------+
5 rows in set (0.00 sec)
他们之间的关系是这样的
左外连接
products p1 LEFT JOIN producers p2
显示products表中所有记录
mysql> SELECT p1.prod_id AS 产品编号,p1.prod_name AS 产品名称,p2.name AS 生产者,p1.prod_price AS 产品价格 FROM products p1 LEFT JOIN producers p2 ON p1.prod_id=p2.prod_id ORDER BY 产品编号;
+--------------+---------------------+-----------+--------------+
| 产品编号 | 产品名称 | 生产者 | 产品价格 |
+--------------+---------------------+-----------+--------------+
| BNBG01 | Fish bean bag toy | jack | 3.49 |
| BNBG01 | Bird bean bag toy | jack | 3.49 |
| BNBG01 | Rabbit bean bag toy | jack | 3.49 |
| BR01 | 8 inch teddy bear | tom | 5.99 |
| BR01 | 12 inch teddy bear | tom | 8.99 |
| BR01 | 18 inch teddy bear | tom | 11.99 |
| RGAN01 | Raggedy Ann | NULL | 4.99 |
| RYL01 | King doll | lucy | 9.49 |
| RYL01 | Queen dool | lucy | 9.49 |
+--------------+---------------------+-----------+--------------+
9 rows in set (0.00 sec)
右外连接
products p1 RIGHT JOIN producers p2
显示producers表中所有记录
mysql> SELECT p1.prod_id AS 产品编号,p1.prod_name AS 产品名称,p2.name AS 生产者,p1.prod_price AS 产品价格 FROM products p1 RIGHT JOIN producers p2 ON p1.prod_id=p2.prod_id ORDER BY 产品编号;
+--------------+---------------------+-----------+--------------+
| 产品编号 | 产品名称 | 生产者 | 产品价格 |
+--------------+---------------------+-----------+--------------+
| BNBG01 | Fish bean bag toy | jack | 3.49 |
| BNBG01 | Bird bean bag toy | jack | 3.49 |
| BNBG01 | Rabbit bean bag toy | jack | 3.49 |
| BR01 | 8 inch teddy bear | tom | 5.99 |
| BR01 | 12 inch teddy bear | tom | 8.99 |
| BR01 | 18 inch teddy bear | tom | 11.99 |
| RYL01 | King doll | lucy | 9.49 |
| RYL01 | Queen dool | lucy | 9.49 |
+--------------+---------------------+-----------+--------------+
8 rows in set (0.00 sec)
子查询
返回单值的子查询
mysql> SELECT * FROM producers WHERE name=(SELECT name FROM producers WHERE age=28);
+----+------+---------+------+
| id | name | prod_id | age |
+----+------+---------+------+
| 1 | jack | BNBG01 | 28 |
+----+------+---------+------+
1 row in set (0.00 sec)
返回多值的子查询
查询价格最低且产品名称不包含（‘Fish bean bag toy’ 和’Rabbit bean bag toy’）的产品信息
mysql> SELECT * from products WHERE prod_price IN (SELECT MIN(prod_price) FROM products) AND prod_name<>'Fish bean bag toy' AND prod_name<>'Rabbit bean bag toy';
+----+---------+-------------------+------------+
| id | prod_id | prod_name | prod_price |
+----+---------+-------------------+------------+
| 2 | BNBG01 | Bird bean bag toy | 3.49 |
+----+---------+-------------------+------------+
1 row in set (0.00 sec)
改变表信息为
mysql> SELECT * FROM products;
+----+---------+---------------------+------------+
| id | prod_id | prod_name | prod_price |
+----+---------+---------------------+------------+
| 1 | BNBG01 | Fish bean bag toy | 3.49 |
| 2 | BNBG01 | Bird bean bag toy | 3.49 |
| 3 | BNBG02 | Rabbit bean bag toy | 3.49 |
| 4 | BR01 | 8 inch teddy bear | 5.99 |
| 5 | BR02 | 12 inch teddy bear | 8.99 |
| 6 | BR03 | 18 inch teddy bear | 11.99 |
| 7 | RGAN01 | Raggedy Ann | 4.99 |
| 8 | RYL01 | King doll | 9.49 |
| 9 | RYL02 | Queen dool | 9.49 |
+----+---------+---------------------+------------+
9 rows in set (0.00 sec)
查询产品价格大于‘BR02’的所有产品信息
mysql> SELECT * FROM products WHERE prod_price>ALL(SELECT prod_price FROM products WHERE prod_id='BR02');
+----+---------+--------------------+------------+
| id | prod_id | prod_name | prod_price |
+----+---------+--------------------+------------+
| 6 | BR03 | 18 inch teddy bear | 11.99 |
| 8 | RYL01 | King doll | 9.49 |
| 9 | RYL02 | Queen dool | 9.49 |
+----+---------+--------------------+------------+
3 rows in set (0.00 sec)
mysql> SELECT * FROM products WHERE prod_price<ALL(SELECT prod_price FROM products WHERE prod_id='BR02');
+----+---------+---------------------+------------+
| id | prod_id | prod_name | prod_price |
+----+---------+---------------------+------------+
| 1 | BNBG01 | Fish bean bag toy | 3.49 |
| 2 | BNBG01 | Bird bean bag toy | 3.49 |
| 3 | BNBG02 | Rabbit bean bag toy | 3.49 |
| 4 | BR01 | 8 inch teddy bear | 5.99 |
| 7 | RGAN01 | Raggedy Ann | 4.99 |
+----+---------+---------------------+------------+
5 rows in set (0.00 sec)
mysql> SELECT * FROM products WHERE prod_price>ANY(SELECT prod_price FROM products WHERE prod_id='BR02');
+----+---------+--------------------+------------+
| id | prod_id | prod_name | prod_price |
+----+---------+--------------------+------------+
| 6 | BR03 | 18 inch teddy bear | 11.99 |
| 8 | RYL01 | King doll | 9.49 |
| 9 | RYL02 | Queen dool | 9.49 |
+----+---------+--------------------+------------+
3 rows in set (0.00 sec)
mysql> SELECT * FROM products WHERE prod_price<ANY(SELECT prod_price FROM products WHERE prod_id='BR02');
+----+---------+---------------------+------------+
| id | prod_id | prod_name | prod_price |
+----+---------+---------------------+------------+
| 1 | BNBG01 | Fish bean bag toy | 3.49 |
| 2 | BNBG01 | Bird bean bag toy | 3.49 |
| 3 | BNBG02 | Rabbit bean bag toy | 3.49 |
| 4 | BR01 | 8 inch teddy bear | 5.99 |
| 7 | RGAN01 | Raggedy Ann | 4.99 |
+----+---------+---------------------+------------+
5 rows in set (0.00 sec)
查询生产者为lucy的产品信息
mysql> SELECT * FROM products WHERE EXISTS (SELECT * FROM producers WHERE products.prod_id=producers.prod_id AND name='lucy');
+----+---------+-----------+------------+
| id | prod_id | prod_name | prod_price |
+----+---------+-----------+------------+
| 8 | RYL01 | King doll | 9.49 |
+----+---------+-----------+------------+
1 row in set (0.00 sec)
相当于
mysql> SELECT * FROM products WHERE prod_id IN (SELECT prod_id FROM producers WHERE products.prod_id=producers.prod_id AND name='lucy');
合并查询结果
mysql> SELECT * FROM products WHERE prod_id='BR01'
-> UNION
-> SELECT * FROM products WHERE prod_price=9.49;
+----+---------+-------------------+------------+
| id | prod_id | prod_name | prod_price |
+----+---------+-------------------+------------+
| 4 | BR01 | 8 inch teddy bear | 5.99 |
| 8 | RYL01 | King doll | 9.49 |
| 9 | RYL02 | Queen dool | 9.49 |
+----+---------+-------------------+------------+
3 rows in set (0.00 sec)
对合并后的查询结果排序
mysql> SELECT * FROM products WHERE prod_id='BR01'
-> UNION
-> SELECT * FROM products WHERE prod_price=9.49
-> ORDER BY prod_id DESC;
+----+---------+-------------------+------------+
| id | prod_id | prod_name | prod_price |
+----+---------+-------------------+------------+
| 9 | RYL02 | Queen dool | 9.49 |
| 8 | RYL01 | King doll | 9.49 |
| 4 | BR01 | 8 inch teddy bear | 5.99 |
+----+---------+-------------------+------------+
3 rows in set (0.00 sec)
ORDER BY之后排序的列名一定是来自第一个表中的列名，第一个表中的列名如果设置了别名，在ORDER BY后面也要写成别名。
mysql> SELECT prod_id AS 产品编号,prod_name,prod_price FROM products WHERE prod_id='BR01'
-> UNION
-> SELECT prod_id,prod_name,prod_price FROM products WHERE prod_price=9.49
-> ORDER BY 产品编号 DESC;
+--------------+-------------------+------------+
| 产品编号 | prod_name | prod_price |
+--------------+-------------------+------------+
| RYL02 | Queen dool | 9.49 |
| RYL01 | King doll | 9.49 |
| BR01 | 8 inch teddy bear | 5.99 |
+--------------+-------------------+------------+
3 rows in set (0.00 sec)
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关系数据库标准语言SQL02