MySQL初步

一写在开头
1.1 本节内容
本节的主要内容是MySQL的基本操作（来自MySQL 5.7官方文档）。

1.2 工具准备
一台装好了mysql的ubuntu 16.04 LTS机器。

二 MySQL的连接与断开
2.1 连接与断开MySQL服务
MySQL提供了一个Linux命令行程序mysql，利用它我们可以连接到MySQL并执行SQL操作。想要查看mysql自带帮助文档，请使用以下命令。

mysql --help

2.2.1 使用以下命令连接到MySQL

mysql -h localhost -u root -p

命令详解：
-h后面参数表示主机名。如果MySQL安装在了本地，后面的参数可以使用localhost表示本地。也可以省略-h参数。
-u后面的参数表示使用的账户名。可以使用root用户，前提是你得记得安装MySQL时输入的root用户密码。
-p参数表示需要输入密码。一般来说-p参数是必须的。

2.1.2 使用quit命令退出mysql命令行

quit

三键入查询语句
3.1 查询MySQL版本和当前时间

SELECT VERSION(), CURRENT_DATE();

+-----------+----------------+

| VERSION() | CURRENT_DATE() |

+-----------+----------------+

| 5.7.21    | 2018-02-14     |

+-----------+----------------+

1 row in set (0.06 sec)

注意：SQL语句后面有个分号，quit命令后没有分号。

3.2 使用MySQL做简单计算

SELECT SIN(PI()/2), (4+1)*5;

+-------------+---------+

| SIN(PI()/2) | (4+1)*5 |

+-------------+---------+

|           1 |      25 |

+-------------+---------+

1 row in set (0.05 sec)

3.3 将多条命令写在同一行

SELECT VERSION(); SELECT NOW();

+-----------+

| VERSION() |

+-----------+

| 5.7.21    |

+-----------+

1 row in set (0.00 sec)

+---------------------+

| NOW()               |

+---------------------+

| 2018-02-14 15:11:56 |

+---------------------+

1 row in set (0.00 sec)

3.4 将一条命令写在多行中

SELECT

USER()

,

CURRENT_DATE();

+----------------+----------------+

| USER()         | CURRENT_DATE() |

+----------------+----------------+

| root@localhost | 2018-02-14     |

+----------------+----------------+

1 row in set (0.05 sec)

注意：在MySQL中，识别一条SQL命令的标志是分号。所以我们可以把一条命令写在多行中。

3.5 撤销当前输入

mysql> SELECT

-> USER()

-> \c

mysql>

注意：c是小写的。

四数据库的创建和使用
4.1 查看当前系统中的数据库

SHOW DATABASES;

+--------------------+

| Database           |

+--------------------+

| information_schema |

| mysql              |

| performance_schema |

| sys                |

+--------------------+

4 rows in set (0.15 sec)

注意：SHOW DATEBASES;只会将当前用户具有的SHOW DATABASES命令权限的数据库打印出来。

4.2 使用（进入)数据库

USE sys

Reading table information for completion of table and column names

You can turn off this feature to get a quicker startup with -A

Database changed

注意：USE和前面的QUIT一样，后面是不接分号的。与之前命令不一样的是USE命令必须写在单独一行中，不能跨越多行。

4.3 创建一个数据库

CREATE DATABASE menagerie;

Query OK, 1 row affected (0.07 sec)

注意：在Linux下数据库名是大小写敏感的。

4.4 在连接MySQL时就指定使用menagerie数据库

mysql -u root -p menagerie

4.5 查看当前使用的是哪个数据库

SELECT DATABASE();

+------------+

| DATABASE() |

+------------+

| menagerie  |

+------------+

1 row in set (0.00 sec)

4.6 查看当前数据库中有哪些表

SELECT TABLES;

Empty set (0.00 sec)

注意：刚刚创建的数据库中是没有表的。

4.7 创建表格

mysql> CREATE TABLE pet

    -> (

    -> name VARCHAR(20),

    -> owner VARCHAR(20),

    -> species VARCHAR(20),

    -> sex CHAR(1),

    -> birth DATE,

    -> death DATE

    -> );

Query OK, 0 rows affected (0.15 sec)

mysql> SHOW TABLES;

+---------------------+

| Tables_in_menagerie |

+---------------------+

| pet                 |

+---------------------+

1 row in set (0.01 sec)

4.8 查看表的信息

mysql> DESCRIBE pet;

+---------+-------------+------+-----+---------+-------+

| Field   | Type        | Null | Key | Default | Extra |

+---------+-------------+------+-----+---------+-------+

| name    | varchar(20) | YES  |     | NULL    |       |

| owner   | varchar(20) | YES  |     | NULL    |       |

| species | varchar(20) | YES  |     | NULL    |       |

| sex     | char(1)     | YES  |     | NULL    |       |

| birth   | date        | YES  |     | NULL    |       |

| death   | date        | YES  |     | NULL    |       |

+---------+-------------+------+-----+---------+-------+

6 rows in set (0.00 sec)

4.9 向表中输入信息
第一步：创建一个pet.sql文件，文件内容如下。

INSERT INTO pet

VALUES ('Fluffy', 'Harold', 'cat', 'f', '1993-02-04', NULL);

INSERT INTO pet

VALUES ('Claws', 'Gwen', 'cat', 'm', '1994-03-17', NULL);

INSERT INTO pet

VALUES ('Buffy', 'Harold', 'dog', 'f', '1989-05-13', NULL);

INSERT INTO pet

VALUES ('Fang', 'Benny', 'dog', 'm', '1990-08-27', NULL);

INSERT INTO pet

VALUES ('Bowser', 'Diane', 'dog', 'm', '1979-08-31', '1995-07-29');

INSERT INTO pet

VALUES ('Chirpy', 'Gwen', 'bird', 'f', '1998-09-11', NULL);

INSERT INTO pet

VALUES ('Whistler', 'Gwen', 'bird', NULL, '1997-12-09', NULL);

INSERT INTO pet

VALUES ('Slim', 'Benny', 'snake', 'm', '1996-04-29', NULL);

INSERT INTO pet

VALUES ('Puffball', 'Diane', 'hamster', 'f', '1999-03-30', NULL);

第二步：使用下列命令执行sql文件，随后查看表的内容。

mysql> source ~/pet.sql

Query OK, 1 row affected (0.13 sec)

Query OK, 1 row affected (0.01 sec)

Query OK, 1 row affected (0.02 sec)

Query OK, 1 row affected (0.01 sec)

Query OK, 1 row affected (0.01 sec)

Query OK, 1 row affected (0.00 sec)

Query OK, 1 row affected (0.00 sec)

Query OK, 1 row affected (0.00 sec)

Query OK, 1 row affected (0.01 sec)

mysql> SELECT * FROM pet;

+----------+--------+---------+------+------------+------------+

| name     | owner  | species | sex  | birth      | death      |

+----------+--------+---------+------+------------+------------+

| Fluffy   | Harold | cat     | f    | 1993-02-04 | NULL       |

| Claws    | Gwen   | cat     | m    | 1994-03-17 | NULL       |

| Buffy    | Harold | dog     | f    | 1989-05-13 | NULL       |

| Fang     | Benny  | dog     | m    | 1990-08-27 | NULL       |

| Bowser   | Diane  | dog     | m    | 1979-08-31 | 1995-07-29 |

| Chirpy   | Gwen   | bird    | f    | 1998-09-11 | NULL       |

| Whistler | Gwen   | bird    | NULL | 1997-12-09 | NULL       |

| Slim     | Benny  | snake   | m    | 1996-04-29 | NULL       |

| Puffball | Diane  | hamster | f    | 1999-03-30 | NULL       |

+----------+--------+---------+------+------------+------------+

9 rows in set (0.00 sec)

五 SELECT语句
5.1 选择所有的列

mysql> SELECT * FROM pet;

+----------+--------+---------+------+------------+------------+

| name     | owner  | species | sex  | birth      | death      |

+----------+--------+---------+------+------------+------------+

| Fluffy   | Harold | cat     | f    | 1993-02-04 | NULL       |

| Claws    | Gwen   | cat     | m    | 1994-03-17 | NULL       |

| Buffy    | Harold | dog     | f    | 1989-05-13 | NULL       |

| Fang     | Benny  | dog     | m    | 1990-08-27 | NULL       |

| Bowser   | Diane  | dog     | m    | 1979-08-31 | 1995-07-29 |

| Chirpy   | Gwen   | bird    | f    | 1998-09-11 | NULL       |

| Whistler | Gwen   | bird    | NULL | 1997-12-09 | NULL       |

| Slim     | Benny  | snake   | m    | 1996-04-29 | NULL       |

| Puffball | Diane  | hamster | f    | 1999-03-30 | NULL       |

+----------+--------+---------+------+------------+------------+

9 rows in set (0.00 sec)

5.2 修改数据

mysql> UPDATE pet SET birth = '1989-08-31' WHERE name = 'Bowser';

Query OK, 1 row affected (0.17 sec)

Rows matched: 1  Changed: 1  Warnings: 0

mysql> SELECT birth FROM pet WHERE name = 'Bowser';

+------------+

| birth      |

+------------+

| 1989-08-31 |

+------------+

1 row in set (0.00 sec)

5.3 清空表内容

mysql> DELETE FROM pet;

Query OK, 9 rows affected (0.08 sec)

mysql> SELECT * FROM pet;

Empty set (0.00 sec)

5.4 选择特定行

mysql> SELECT * FROM pet WHERE name = 'Bowser';

+--------+-------+---------+------+------------+------------+

| name   | owner | species | sex  | birth      | death      |

+--------+-------+---------+------+------------+------------+

| Bowser | Diane | dog     | m    | 1989-08-31 | 1995-07-29 |

+--------+-------+---------+------+------------+------------+

1 row in set (0.00 sec)

5.5 根据条件选择

mysql> SELECT * FROM pet WHERE birth >= '1998-1-1';

+----------+-------+---------+------+------------+-------+

| name     | owner | species | sex  | birth      | death |

+----------+-------+---------+------+------------+-------+

| Chirpy   | Gwen  | bird    | f    | 1998-09-11 | NULL  |

| Puffball | Diane | hamster | f    | 1999-03-30 | NULL  |

+----------+-------+---------+------+------------+-------+

2 rows in set (0.00 sec)

5.6 根据组合条件选择
5.6.1

mysql> SELECT * FROM pet WHERE species = 'dog' AND sex = 'f';

+-------+--------+---------+------+------------+-------+

| name  | owner  | species | sex  | birth      | death |

+-------+--------+---------+------+------------+-------+

| Buffy | Harold | dog     | f    | 1989-05-13 | NULL  |

+-------+--------+---------+------+------------+-------+

1 row in set (0.04 sec)

5.6.2

mysql> SELECT * FROM pet WHERE

    -> (species = 'cat' AND sex = 'm')

    -> OR (species = 'dog' AND sex = 'f');

+-------+--------+---------+------+------------+-------+

| name  | owner  | species | sex  | birth      | death |

+-------+--------+---------+------+------------+-------+

| Claws | Gwen   | cat     | m    | 1994-03-17 | NULL  |

| Buffy | Harold | dog     | f    | 1989-05-13 | NULL  |

+-------+--------+---------+------+------------+-------+

2 rows in set (0.00 sec)

注意：AND优先级高于OR。

5.7 选择特定列
5.7.1

mysql> SELECT name, birth FROM pet;

+----------+------------+

| name     | birth      |

+----------+------------+

| Fluffy   | 1993-02-04 |

| Claws    | 1994-03-17 |

| Buffy    | 1989-05-13 |

| Fang     | 1990-08-27 |

| Bowser   | 1989-08-31 |

| Chirpy   | 1998-09-11 |

| Whistler | 1997-12-09 |

| Slim     | 1996-04-29 |

| Puffball | 1999-03-30 |

+----------+------------+

9 rows in set (0.00 sec)

5.7.2

mysql> SELECT owner FROM pet;

+--------+

| owner  |

+--------+

| Harold |

| Gwen   |

| Harold |

| Benny  |

| Diane  |

| Gwen   |

| Gwen   |

| Benny  |

| Diane  |

+--------+

9 rows in set (0.00 sec)

5.7.3 过滤重复项，使重复项仅出现一次

mysql> SELECT DISTINCT owner FROM pet;

+--------+

| owner  |

+--------+

| Harold |

| Gwen   |

| Benny  |

| Diane  |

+--------+

4 rows in set (0.05 sec)

5.8 选择特定的行与列

mysql> SELECT name, species, birth FROM pet

    -> WHERE species = 'dog' OR species = 'cat';

+--------+---------+------------+

| name   | species | birth      |

+--------+---------+------------+

| Fluffy | cat     | 1993-02-04 |

| Claws  | cat     | 1994-03-17 |

| Buffy  | dog     | 1989-05-13 |

| Fang   | dog     | 1990-08-27 |

| Bowser | dog     | 1989-08-31 |

+--------+---------+------------+

5 rows in set (0.00 sec)

5.9 对输出结果进行排序

mysql> SELECT name, birth FROM pet ORDER BY birth;

+----------+------------+

| name     | birth      |

+----------+------------+

| Buffy    | 1989-05-13 |

| Bowser   | 1989-08-31 |

| Fang     | 1990-08-27 |

| Fluffy   | 1993-02-04 |

| Claws    | 1994-03-17 |

| Slim     | 1996-04-29 |

| Whistler | 1997-12-09 |

| Chirpy   | 1998-09-11 |

| Puffball | 1999-03-30 |

+----------+------------+

9 rows in set (0.00 sec)

5.10 使用DESC关键字进行降序排列

mysql> SELECT name, birth FROM pet ORDER BY birth DESC;

+----------+------------+

| name     | birth      |

+----------+------------+

| Puffball | 1999-03-30 |

| Chirpy   | 1998-09-11 |

| Whistler | 1997-12-09 |

| Slim     | 1996-04-29 |

| Claws    | 1994-03-17 |

| Fluffy   | 1993-02-04 |

| Fang     | 1990-08-27 |

| Bowser   | 1989-08-31 |

| Buffy    | 1989-05-13 |

+----------+------------+

9 rows in set (0.00 sec)

5.11 对多个列使用不同的排序顺序

mysql> SELECT name, species, birth FROM pet ORDER BY species, birth DESC;

+----------+---------+------------+

| name     | species | birth      |

+----------+---------+------------+

| Chirpy   | bird    | 1998-09-11 |

| Whistler | bird    | 1997-12-09 |

| Claws    | cat     | 1994-03-17 |

| Fluffy   | cat     | 1993-02-04 |

| Fang     | dog     | 1990-08-27 |

| Bowser   | dog     | 1989-08-31 |

| Buffy    | dog     | 1989-05-13 |

| Puffball | hamster | 1999-03-30 |

| Slim     | snake   | 1996-04-29 |

+----------+---------+------------+

9 rows in set (0.00 sec)

六常用的计算函数
6.1 TIMESTAMPDIFF()函数
6.1.1 TIMESTAMPDIFF()

mysql> SELECT name, birth, CURDATE(),

    -> TIMESTAMPDIFF(YEAR, birth, CURDATE()) AS age

    -> FROM pet;

+----------+------------+------------+------+

| name     | birth      | CURDATE()  | age  |

+----------+------------+------------+------+

| Fluffy   | 1993-02-04 | 2018-02-15 |   25 |

| Claws    | 1994-03-17 | 2018-02-15 |   23 |

| Buffy    | 1989-05-13 | 2018-02-15 |   28 |

| Fang     | 1990-08-27 | 2018-02-15 |   27 |

| Bowser   | 1989-08-31 | 2018-02-15 |   28 |

| Chirpy   | 1998-09-11 | 2018-02-15 |   19 |

| Whistler | 1997-12-09 | 2018-02-15 |   20 |

| Slim     | 1996-04-29 | 2018-02-15 |   21 |

| Puffball | 1999-03-30 | 2018-02-15 |   18 |

+----------+------------+------------+------+

9 rows in set (0.05 sec)

6.1.2 排序

mysql> SELECT name, birth, CURDATE(),

    -> TIMESTAMPDIFF(YEAR, birth, CURDATE()) AS age

    -> FROM pet ORDER BY name;

+----------+------------+------------+------+

| name     | birth      | CURDATE()  | age  |

+----------+------------+------------+------+

| Bowser   | 1989-08-31 | 2018-02-15 |   28 |

| Buffy    | 1989-05-13 | 2018-02-15 |   28 |

| Chirpy   | 1998-09-11 | 2018-02-15 |   19 |

| Claws    | 1994-03-17 | 2018-02-15 |   23 |

| Fang     | 1990-08-27 | 2018-02-15 |   27 |

| Fluffy   | 1993-02-04 | 2018-02-15 |   25 |

| Puffball | 1999-03-30 | 2018-02-15 |   18 |

| Slim     | 1996-04-29 | 2018-02-15 |   21 |

| Whistler | 1997-12-09 | 2018-02-15 |   20 |

+----------+------------+------------+------+

9 rows in set (0.00 sec)

6.1.3 计算寿命

mysql> SELECT name, birth, death,

    -> TIMESTAMPDIFF(YEAR, birth, death) AS age

    -> FROM pet WHERE death IS NOT NULL ORDER BY age;

+--------+------------+------------+------+

| name   | birth      | death      | age  |

+--------+------------+------------+------+

| Bowser | 1989-08-31 | 1995-07-29 |    5 |

+--------+------------+------------+------+

1 row in set (0.00 sec)

注意：NULL是一个特殊的值，判断值不为空（即不为NULL）需要使用death IS NOT NULL，而不能使用death <> NULL。

6.2 MONTH()函数
6.2.1 MONTH()

mysql> SELECT name, birth, MONTH(birth) FROM pet;

+----------+------------+--------------+

| name     | birth      | MONTH(birth) |

+----------+------------+--------------+

| Fluffy   | 1993-02-04 |            2 |

| Claws    | 1994-03-17 |            3 |

| Buffy    | 1989-05-13 |            5 |

| Fang     | 1990-08-27 |            8 |

| Bowser   | 1989-08-31 |            8 |

| Chirpy   | 1998-09-11 |            9 |

| Whistler | 1997-12-09 |           12 |

| Slim     | 1996-04-29 |            4 |

| Puffball | 1999-03-30 |            3 |

+----------+------------+--------------+

9 rows in set (0.00 sec)

注意：受上面结果的启发，YEAR(birth)，DAYOFMONTH(birth)的结果是什么呢？

6.2.2 找到5月出生的动物

mysql> SELECT name, birth FROM pet WHERE MONTH(birth) = 5;

+-------+------------+

| name  | birth      |

+-------+------------+

| Buffy | 1989-05-13 |

+-------+------------+

1 row in set (0.05 sec)

6.2.3 DATE_ADD()

mysql> SELECT name, birth FROM pet

    -> WHERE MONTH(birth) = MONTH(DATE_ADD(CURDATE(), INTERVAL 1 MONTH));

+----------+------------+

| name     | birth      |

+----------+------------+

| Claws    | 1994-03-17 |

| Puffball | 1999-03-30 |

+----------+------------+

2 rows in set (0.08 sec)

6.3 如何处理为空值

mysql> SELECT 1 IS NULL, 1 IS NOT NULL;

+-----------+---------------+

| 1 IS NULL | 1 IS NOT NULL |

+-----------+---------------+

|         0 |             1 |

+-----------+---------------+

1 row in set (0.00 sec)

七模式匹配
7.1 匹配规则
_（下划线）- 表示单个字符
%（百分号） - 表示任意个字符

注意：模式匹配时是大小写敏感的，匹配使用的运算符是LIKE和NOT LIKE。不能使用数学运算符。

7.2 小例子
7.2.1 找到以字母b开头的宠物

mysql> SELECT * FROM pet WHERE name LIKE 'b%';

+--------+--------+---------+------+------------+------------+

| name   | owner  | species | sex  | birth      | death      |

+--------+--------+---------+------+------------+------------+

| Buffy  | Harold | dog     | f    | 1989-05-13 | NULL       |

| Bowser | Diane  | dog     | m    | 1989-08-31 | 1995-07-29 |

+--------+--------+---------+------+------------+------------+

2 rows in set (0.00 sec)

7.2.2 找到以fy结尾的宠物

mysql> SELECT * FROM pet WHERE name LIKE '%fy';

+--------+--------+---------+------+------------+-------+

| name   | owner  | species | sex  | birth      | death |

+--------+--------+---------+------+------------+-------+

| Fluffy | Harold | cat     | f    | 1993-02-04 | NULL  |

| Buffy  | Harold | dog     | f    | 1989-05-13 | NULL  |

+--------+--------+---------+------+------------+-------+

2 rows in set (0.00 sec)

7.2.3 找到名字中含有字母w的宠物

mysql> SELECT * FROM pet WHERE name LIKE '%w%';

+----------+-------+---------+------+------------+------------+

| name     | owner | species | sex  | birth      | death      |

+----------+-------+---------+------+------------+------------+

| Claws    | Gwen  | cat     | m    | 1994-03-17 | NULL       |

| Bowser   | Diane | dog     | m    | 1989-08-31 | 1995-07-29 |

| Whistler | Gwen  | bird    | NULL | 1997-12-09 | NULL       |

+----------+-------+---------+------+------------+------------+

3 rows in set (0.00 sec)

7.2.4 找到名字为5个字符的宠物

mysql> SELECT * FROM pet WHERE name LIKE '_____';

+-------+--------+---------+------+------------+-------+

| name  | owner  | species | sex  | birth      | death |

+-------+--------+---------+------+------------+-------+

| Claws | Gwen   | cat     | m    | 1994-03-17 | NULL  |

| Buffy | Harold | dog     | f    | 1989-05-13 | NULL  |

+-------+--------+---------+------+------------+-------+

2 rows in set (0.00 sec)

八行计数
8.1 COUNT()函数
8.1.1 共有多少宠物

mysql> SELECT COUNT(*) FROM pet;

+----------+

| COUNT(*) |

+----------+

|        9 |

+----------+

1 row in set (0.04 sec)

8.1.2 每个主人共有几只宠物

mysql> SELECT owner, COUNT(*) FROM pet GROUP BY owner;

+--------+----------+

| owner  | COUNT(*) |

+--------+----------+

| Benny  |        2 |

| Diane  |        2 |

| Gwen   |        3 |

| Harold |        2 |

+--------+----------+

4 rows in set (0.05 sec)

8.1.3 每个物种共有几只宠物

mysql> SELECT species, COUNT(*) FROM pet GROUP BY species;

+---------+----------+

| species | COUNT(*) |

+---------+----------+

| bird    |        2 |

| cat     |        2 |

| dog     |        3 |

| hamster |        1 |

| snake   |        1 |

+---------+----------+

5 rows in set (0.01 sec)

8.1.4 每种性别共有几只宠物

mysql> SELECT sex, COUNT(*) FROM pet GROUP BY sex;

+------+----------+

| sex  | COUNT(*) |

+------+----------+

| NULL |        1 |

| f    |        4 |

| m    |        4 |

+------+----------+

3 rows in set (0.00 sec)

8.1.5 每种物种和性别共有几只宠物

mysql> SELECT species, sex, COUNT(*) FROM pet GROUP BY species, sex;

+---------+------+----------+

| species | sex  | COUNT(*) |

+---------+------+----------+

| bird    | NULL |        1 |

| bird    | f    |        1 |

| cat     | f    |        1 |

| cat     | m    |        1 |

| dog     | f    |        1 |

| dog     | m    |        2 |

| hamster | f    |        1 |

| snake   | m    |        1 |

+---------+------+----------+

8 rows in set (0.00 sec)

8.1.6 只考虑狗和猫的情况下，每种物种和性别共有几只宠物

mysql> SELECT species, sex, COUNT(*) FROM pet

    -> WHERE species = 'dog' OR species = 'cat'

    -> GROUP BY species, sex;

+---------+------+----------+

| species | sex  | COUNT(*) |

+---------+------+----------+

| cat     | f    |        1 |

| cat     | m    |        1 |

| dog     | f    |        1 |

| dog     | m    |        2 |

+---------+------+----------+

4 rows in set (0.06 sec)

8.1.7 排除性别未知的宠物情况下，每种物种和性别共有几只宠物

mysql> SELECT species, sex, COUNT(*) FROM pet

    -> WHERE sex IS NOT NULL

    -> GROUP BY species, sex;

+---------+------+----------+

| species | sex  | COUNT(*) |

+---------+------+----------+

| bird    | f    |        1 |

| cat     | f    |        1 |

| cat     | m    |        1 |

| dog     | f    |        1 |

| dog     | m    |        2 |

| hamster | f    |        1 |

| snake   | m    |        1 |

+---------+------+----------+

7 rows in set (0.00 sec)

九使用多个表
9.1 创建一个event表以记录宠物的其他信息

mysql> CREATE TABLE event                                                           -> (

    -> name VARCHAR(20),

    -> date DATE,

    -> type VARCHAR(15),

    -> remark VARCHAR(255)

    -> );

Query OK, 0 rows affected (0.49 sec)

9.2 往表中插入数据

INSERT INTO event

VALUES ('Fluffy', '1995-05-15', 'litter', '4 kittens, 3 female, 1 male');

INSERT INTO event

VALUES ('Buffy', '1993-06-23', 'litter', '5 puppies, 2 female, 3 male');

INSERT INTO event

VALUES ('Buffy', '1994-06-19', 'litter', '3 puppies, 3 female');

INSERT INTO event

VALUES ('Chirpy', '1999-03-21', 'vet', 'needed beak straightened');

INSERT INTO event

VALUES ('Slim', '1997-08-03', 'vet', 'broken rib');

INSERT INTO event

VALUES ('Bowser', '1991-10-12', 'kennel', NULL);

INSERT INTO event

VALUES ('Fang', '1991-10-12', 'kennel', NULL);

INSERT INTO event

VALUES ('Fang', '1998-08-28', 'birthday', 'Gave him a new chew toy');

INSERT INTO event

VALUES ('Claws', '1998-03-17', 'birthday', 'Gave him a new flea collar');

INSERT INTO event

VALUES ('Whistler', '1998-12-09', 'birthday', 'First birthday');

9.3 多表连接
9.3.1

mysql> SELECT pet.name

    -> ,

    -> (YEAR(date)-YEAR(birth)) - (RIGHT(date, 5) < RIGHT(birth, 5)) AS age,

    -> remark

    -> FROM pet INNER JOIN event

    -> ON pet.name = event.name

    -> WHERE event.type = 'litter';

+--------+------+-----------------------------+

| name   | age  | remark                      |

+--------+------+-----------------------------+

| Fluffy |    2 | 4 kittens, 3 female, 1 male |

| Buffy  |    4 | 5 puppies, 2 female, 3 male |

| Buffy  |    5 | 3 puppies, 3 female         |

+--------+------+-----------------------------+

3 rows in set (0.16 sec)

9.3.2

mysql> SELECT p1.name, p1.sex, p2.name, p2.sex, p1.species

    -> FROM pet AS p1 INNER JOIN pet AS p2

    -> ON p1.species = p2.species AND p1.sex = 'f' AND p2.sex = 'm';

+--------+------+--------+------+---------+

| name   | sex  | name   | sex  | species |

+--------+------+--------+------+---------+

| Fluffy | f    | Claws  | m    | cat     |

| Buffy  | f    | Fang   | m    | dog     |

| Buffy  | f    | Bowser | m    | dog     |

+--------+------+--------+------+---------+

3 rows in set (0.00 sec)

十获取数据库信息
10.1

语句	功能
SHOW DATABASES;	显示MySQL Server所管理的数据库
SELECT DATABASE();	当前选择的是哪个数据库
SHOW TABLES;	当前数据库中有哪些表
DESCRIBE pet;	显示pet表的表结构

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