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 |