MySQL入门（参考官网）
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目录
一、登陆和退出
1. 远程主机
shell> mysql -h host -u user -p
Enter password: ********
Welcome to the MySQL monitor. Commands end with ; or g.
mysql>2. 登陆本机
shell> mysql -u user -p3. 退出mysql
mysql> QUIT二、输入查询
查询版本号和当前日期
mysql> SELECT VERSION(), CURRENT_DATE;
+-----------+--------------+
| VERSION() | CURRENT_DATE |
+-----------+--------------+
| 5.7.24 | 2018-11-12 |
+-----------+--------------+
1 row in set (0.01 sec)
mysql>大小写不敏感
把mysql当计算器用
mysql> SELECT SIN(PI()/4), (4+1)*5;
+--------------------+---------+
| SIN(PI()/4) | (4+1)*5 |
+--------------------+---------+
| 0.7071067811865476 | 25 |
+--------------------+---------+
1 row in set (0.01 sec)在一行上输入多个语句。分号结束每一个命令:
mysql> SELECT VERSION(); SELECT NOW();
+-----------+
| VERSION() |
+-----------+
| 5.7.24 |
+-----------+
1 row in set (0.00 sec)
+---------------------+
| NOW() |
+---------------------+
| 2018-11-13 00:10:14 |
+---------------------+
1 row in set (0.00 sec)mysql 通过 查找终止分号;来确定语句的结束位置
mysql> SELECT
-> USER()
-> ,
-> CURRENT_DATE;
+----------------+--------------+
| USER() | CURRENT_DATE |
+----------------+--------------+
| [email protected] | 2018-11-13 |
+----------------+--------------+
1 row in set (0.00 sec)
mysql> SELECT USER(),CURRENT_DATE;
+----------------+--------------+
| USER() | CURRENT_DATE |
+----------------+--------------+
| [email protected] | 2018-11-13 |
+----------------+--------------+
1 row in set (0.00 sec)通过键入以下内容取消该查询:c
mysql> SELECT
-> USER()
-> c三、创建和使用数据库
展示存在的数据库
mysql> SHOW DATABASES;
+--------------------+
| Database |
+--------------------+
| information_schema |
| falcon |
| mysql |
| performance_schema |
| sys |
+--------------------+使用数据库
mysql> USE test
Database changedshell> mysql -h host -u user -p menagerie
Enter password: ********3.1 创建和选择数据库
mysql> CREATE DATABASE menagerie;mysql> USE menagerie
Database changed3.2 创建表
mysql> SHOW TABLES;
Empty set (0.00 sec)创建表
mysql> CREATE TABLE pet (name VARCHAR(20), owner VARCHAR(20),
-> species VARCHAR(20), sex CHAR(1), birth DATE, death DATE);展示表单：
mysql> SHOW TABLES;
+---------------------+
| Tables_in_menagerie |
+---------------------+
| pet |
+---------------------+
1 row in set (0.00 sec)描述表单
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 (0.01 sec)3.3 将数据加载到表中
建立表格以后需要：
| name | owner | species | sex | birth | death |
|---|---|---|---|---|---|
| Fluffy | Harold | cat | f | 1993-02-04 | |
| Claws | Gwen | cat | m | 1994-03-17 | |
| Buffy | Harold | dog | f | 1989-05-13 | |
| Fang | Benny | dog | m | 1990-08-27 | |
| Bowser | Diane | dog | m | 1979-08-31 | 1995-07-29 |
| Chirpy | Gwen | bird | f | 1998-09-11 | |
| Whistler | Gwen | bird | 1997-12-09 | ||
| Slim | Benny | snake | m | 1996-04-29 |
保存为pet.txt
从excel中直接复制到pet.txt,空值用N 表示
Whistler Gwen bird N 1997-12-09 N
3.3.1 导入数据
LOAD DATA LOCAL INFILE ‘D:/Temp/pet.txt‘ INTO TABLE pet;win编辑器
mysql> LOAD DATA LOCAL INFILE ‘/path/pet.txt‘ INTO TABLE pet
-> LINES TERMINATED BY ‘
‘;在运行 os x 的 apple 计算机上, 您可能想要使用。LINES TERMINATED BY ‘ ‘
3.3.2 插入语句
mysql> INSERT INTO pet
-> VALUES (‘Puffball‘,‘Diane‘,‘hamster‘,‘f‘,‘1999-03-30‘,NULL);3.4 操作表格
SELECT 语法：
SELECT what_to_select
FROM which_table
WHERE conditions_to_satisfy;3.4.1 查询所有数据
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 |
+----------+--------+---------+------+------------+------------+update 语句修复错误记录 :
mysql> UPDATE pet SET birth = ‘1989-08-31‘ WHERE name = ‘Bowser‘;3.4.2 查询某行
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 |
+--------+-------+---------+------+------------+------------+选择特定条件：
mysql> SELECT * FROM pet WHERE birth >= ‘1998-1-1‘;
+----------+-------+---------+------+------------+------------+
| name | owner | species | sex | birth | death |
+----------+-------+---------+------+------------+------------+
| Chirpy | Gwen | bird | f | 1998-09-11 | 0000-00-00 |
| Puffball | Diane | hamster | f | 1999-03-30 | NULL |
+----------+-------+---------+------+------------+------------+条件and：
mysql> SELECT * FROM pet WHERE species = ‘dog‘ AND sex = ‘f‘;
+-------+--------+---------+------+------------+------------+
| name | owner | species | sex | birth | death |
+-------+--------+---------+------+------------+------------+
| Buffy | Harold | dog | f | 1989-05-13 | 0000-00-00 |
+-------+--------+---------+------+------------+------------+条件or：
mysql> SELECT * FROM pet WHERE species = ‘snake‘ OR species = ‘bird‘;
+----------+-------+---------+------+------------+------------+
| name | owner | species | sex | birth | death |
+----------+-------+---------+------+------------+------------+
| Chirpy | Gwen | bird | f | 1998-09-11 | 0000-00-00 |
| Whistler | Gwen | bird | | 1997-12-09 | 0000-00-00 |
| Slim | Benny | snake | m | 1996-04-29 | 0000-00-00 |
+----------+-------+---------+------+------------+------------+and 、 or 混合使用：
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 | 0000-00-00 |
| Buffy | Harold | dog | f | 1989-05-13 | 0000-00-00 |
+-------+--------+---------+------+------------+------------+3.4.3 查询某列
选择某列，按照 ，分隔
mysql> SELECT name`,` birth FROM pet;
+----------+------------+
| name | birth |
+----------+------------+
| name | 0000-00-00 |
| 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 |
+----------+------------+选择动物主人：
mysql> SELECT owner FROM pet;
+--------+
| owner |
+--------+
| owner |
| Harold |
| Gwen |
| Harold |
| Benny |
| Diane |
| Gwen |
| Gwen |
| Benny |
| Diane |
+--------+使用DISTINCT去重
mysql> SELECT DISTINCT owner FROM pet;
+--------+
| owner |
+--------+
| owner |
| Harold |
| Gwen |
| Benny |
| Diane |
+--------+使用WHERE条件查询
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 |
+--------+---------+------------+3.4.4 排序行
使用ORDER BY ,默认升序
mysql> SELECT name, birth FROM pet ORDER BY birth;
+----------+------------+
| name | birth |
+----------+------------+
| name | 0000-00-00 |
| 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 |
+----------+------------+默认不区分大小写排序，如果要区分使用：
ORDER BY BINARY col_name
BINARY：转换为二进制字符,方便排序
使用ORDER BY ,默认升序，如果降序，添加DESC
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 |
| name | 0000-00-00 |
+----------+------------+多个列排序：
先按照动物种类升序，然后按照出生日期降序
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 |
| name | species | 0000-00-00 |
+----------+---------+------------+3.4.5 ?日期计算
TIMESTAMPDIFF()：时间差函数
mysql> SELECT TIMESTAMPDIFF(YEAR,‘1989-08-31‘,CURDATE());
+--------------------------------------------+
| TIMESTAMPDIFF(YEAR,‘1989-08-31‘,CURDATE()) |
+--------------------------------------------+
| 29 |
+--------------------------------------------+常用时间函数：
mysql> SELECT NOW(),CURDATE(),CURTIME();
+---------------------+------------+-----------+
| NOW() | CURDATE() | CURTIME() |
+---------------------+------------+-----------+
| 2018-11-13 10:21:28 | 2018-11-13 | 10:21:28 |
+---------------------+------------+-----------+
查询显示每个宠物的出生日期、当前日期，用age做别名
mysql> SELECT name, birth, CURDATE(),
-> TIMESTAMPDIFF(YEAR,birth,CURDATE()) AS age
-> FROM pet;
+----------+------------+------------+------+
| name | birth | CURDATE() | age |
+----------+------------+------------+------+
| Fluffy | 1993-02-04 | 2018-11-13 | 25 |
| Claws | 1994-03-17 | 2018-11-13 | 24 |
| Buffy | 1989-05-13 | 2018-11-13 | 29 |
| Fang | 1990-08-27 | 2018-11-13 | 28 |
| Bowser | 1989-08-31 | 2018-11-13 | 29 |
| Chirpy | 1998-09-11 | 2018-11-13 | 20 |
| Whistler | 1997-12-09 | 2018-11-13 | 20 |
| Slim | 1996-04-29 | 2018-11-13 | 22 |
| Puffball | 1999-03-30 | 2018-11-13 | 19 |
+----------+------------+------------+------+
查询同时 按照姓名排序
mysql> SELECT name, birth, CURDATE(),
-> TIMESTAMPDIFF(YEAR,birth,CURDATE()) AS age
-> FROM pet ORDER BY name;
+----------+------------+------------+------+
| name | birth | CURDATE() | age |
+----------+------------+------------+------+
| Bowser | 1989-08-31 | 2018-11-13 | 29 |
| Buffy | 1989-05-13 | 2018-11-13 | 29 |
| Chirpy | 1998-09-11 | 2018-11-13 | 20 |
| Claws | 1994-03-17 | 2018-11-13 | 24 |
| Fang | 1990-08-27 | 2018-11-13 | 28 |
| Fluffy | 1993-02-04 | 2018-11-13 | 25 |
| Puffball | 1999-03-30 | 2018-11-13 | 19 |
| Slim | 1996-04-29 | 2018-11-13 | 22 |
| Whistler | 1997-12-09 | 2018-11-13 | 20 |
+----------+------------+------------+------+查询同时 按照年龄排序
mysql> SELECT name, birth, CURDATE(),
-> TIMESTAMPDIFF(YEAR,birth,CURDATE()) AS age
-> FROM pet ORDER BY age;
+----------+------------+------------+------+
| name | birth | CURDATE() | age |
+----------+------------+------------+------+
| Puffball | 1999-03-30 | 2018-11-13 | 19 |
| Chirpy | 1998-09-11 | 2018-11-13 | 20 |
| Whistler | 1997-12-09 | 2018-11-13 | 20 |
| Slim | 1996-04-29 | 2018-11-13 | 22 |
| Claws | 1994-03-17 | 2018-11-13 | 24 |
| Fluffy | 1993-02-04 | 2018-11-13 | 25 |
| Fang | 1990-08-27 | 2018-11-13 | 28 |
| Buffy | 1989-05-13 | 2018-11-13 | 29 |
| Bowser | 1989-08-31 | 2018-11-13 | 29 |
+----------+------------+------------+------+查询已经死亡的宠物
把默认导入的数值从‘0000-00-00‘ 改成‘NUll‘
UPDATE pet SET death = NULL WHERE death= 0000-00-00;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 |
+--------+------------+------------+------+MySQL 的一些日期函数：
YEAR()：返回年
MONTH()：返回月
DAYOFMONTH()：返回日
DATE_ADD() ：添加时间
?
mysql> SELECT YEAR(‘1987-01-01‘);
+--------------------+
| YEAR(‘1987-01-01‘) |
+--------------------+
| 1987 |
+--------------------+mysql> SELECT MONTH(‘2008-02-03‘);
+---------------------+
| MONTH(‘2008-02-03‘) |
+---------------------+
| 2 |
+---------------------+mysql> SELECT MONTHNAME(‘2008-02-03‘);
+-------------------------+
| MONTHNAME(‘2008-02-03‘) |
+-------------------------+
| February |
+-------------------------+现在是今年的 多少天 多少周
mysql> SELECT DAYOFYEAR(now()),WEEKOFYEAR(now());
+------------------+-------------------+
| DAYOFYEAR(now()) | WEEKOFYEAR(now()) |
+------------------+-------------------+
| 317 | 46 |
+------------------+-------------------+2008-01-03第多少天，多少周
mysql> SELECT DAYOFYEAR(‘2008-01-03‘),WEEKOFYEAR(‘2008-01-03‘);
+-------------------------+--------------------------+
| DAYOFYEAR(‘2008-01-03‘) | WEEKOFYEAR(‘2008-01-03‘) |
+-------------------------+--------------------------+
| 3 | 1 |
+-------------------------+--------------------------+查询宠物出生月
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 |
+----------+------------+--------------+查询5月出生的宠物
mysql> SELECT name, birth FROM pet WHERE MONTH(birth) = 5;
+-------+------------+
| name | birth |
+-------+------------+
| Buffy | 1989-05-13 |
+-------+------------+2018-05-01 添加1天
mysql> SELECT DATE_ADD(‘2018-05-01‘,INTERVAL 1 DAY);
+---------------------------------------+
| DATE_ADD(‘2018-05-01‘,INTERVAL 1 DAY) |
+---------------------------------------+
| 2018-05-02 |
+---------------------------------------+查询下个月是哪个月
mysql> SELECT MONTH(DATE_ADD(CURDATE(),INTERVAL 1 MONTH));
+---------------------------------------------+
| MONTH(DATE_ADD(CURDATE(),INTERVAL 1 MONTH)) |
+---------------------------------------------+
| 12 |
+---------------------------------------------+查询即将生日的宠物，距离目前最近的一个月
- 方法1：当前月份+1个月
mysql> SELECT name, birth FROM pet
-> WHERE MONTH(birth) = MONTH(DATE_ADD(CURDATE(),INTERVAL 1 MONTH));
+----------+------------+
| name | birth |
+----------+------------+
| Whistler | 1997-12-09 |
+----------+------------+- 方法2：当前月份取余+1
mysql> SELECT name, birth FROM pet
-> WHERE MONTH(birth) = MOD(MONTH(CURDATE()), 12) + 1;
+----------+------------+
| name | birth |
+----------+------------+
| Whistler | 1997-12-09 |
+----------+------------+- MOD(12, 5)
mysql> SELECT MOD(12, 5);
+------------+
| MOD(12, 5) |
+------------+
| 2 |
+------------+3.4.6 使用空值
NULL value ：a missing unknown value，要和其他值区别对待
测试NULL，使用
mysql> SELECT 1 IS NULL, 1 IS NOT NULL;
+-----------+---------------+
| 1 IS NULL | 1 IS NOT NULL |
+-----------+---------------+
| 0 | 1 |
+-----------+---------------+mysql> SELECT 0 IS NULL, 0 IS NOT NULL, ‘‘ IS NULL, ‘‘ IS NOT NULL;
+-----------+---------------+------------+----------------+
| 0 IS NULL | 0 IS NOT NULL | ‘‘ IS NULL | ‘‘ IS NOT NULL |
+-----------+---------------+------------+----------------+
| 0 | 1 | 0 | 1 |
+-----------+---------------+------------+----------------+不能使用算术笔记用算符判断
null
=, <, or <>3.4.7 匹配方式
- 标准的 sql 模式匹配
- 正则表达式的模式匹配
- 默认不区分大小写
标准匹配
使用：
查找b开头的名字：
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 |
+--------+--------+---------+------+------------+------------+查找fy结尾的名字：
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 |查找名字包含一个w:
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 |
+----------+-------+---------+------+------------+------------+查找名字是5个字符的：
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 |
+-------+--------+---------+------+------------+-------+正则匹配
使用：
RLIKENOT RLIKE和上述等价
查找b开头的名字：
mysql> SELECT * FROM pet WHERE name REGEXP ‘^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 |
+--------+--------+---------+------+------------+------------+若要强制regexp比较区分大小写, 请使用binary关键字将其中一个字符串设置为二进制字符串。
匹配名称由小写:b开头
SELECT * FROM pet WHERE name REGEXP BINARY ‘^b‘;查找fy结尾的名字：
mysql> SELECT * FROM pet WHERE name REGEXP ‘fy$‘;
+--------+--------+---------+------+------------+-------+
| name | owner | species | sex | birth | death |
+--------+--------+---------+------+------------+-------+
| Fluffy | Harold | cat | f | 1993-02-04 | NULL |
| Buffy | Harold | dog | f | 1989-05-13 | NULL |
+--------+--------+---------+------+------------+-------+查找名字包含一个w:
mysql> SELECT * FROM pet WHERE name REGEXP ‘w‘;
+----------+-------+---------+------+------------+------------+
| name | owner | species | sex | birth | death |
+----------+-------+---------+------+------------+------------+
| Claws | Gwen | cat | m | 1994-03-17 | NULL |
| Bowser | Diane | dog | m | 1989-08-31 | 1995-07-29 |
| Whistler | Gwen | bird | NULL | 1997-12-09 | NULL |
+----------+-------+---------+------+------------+------------+查找名字是5个字符的
mysql> SELECT * FROM pet WHERE name REGEXP ‘^.....$‘;
+-------+--------+---------+------+------------+-------+
| name | owner | species | sex | birth | death |
+-------+--------+---------+------+------------+-------+
| Claws | Gwen | cat | m | 1994-03-17 | NULL |
| Buffy | Harold | dog | f | 1989-05-13 | NULL |
+-------+--------+---------+------+------------+-------+或者^.{5}$ ：^开头$结尾
mysql> SELECT * FROM pet WHERE name REGEXP ‘^.{5}$‘;
+-------+--------+---------+------+------------+-------+
| name | owner | species | sex | birth | death |
+-------+--------+---------+------+------------+-------+
| Claws | Gwen | cat | m | 1994-03-17 | NULL |
| Buffy | Harold | dog | f | 1989-05-13 | NULL |
+-------+--------+---------+------+------------+-------+3.4.8 统计行
COUNT(*) 统计函数
统计行数
mysql> SELECT COUNT(*) FROM pet;
+----------+
| COUNT(*) |
+----------+
| 9 |
+----------+统计每个人有多少只宠物
mysql> SELECT owner, COUNT(*) FROM pet GROUP BY owner;
+--------+----------+
| owner | COUNT(*) |
+--------+----------+
| Benny | 2 |
| Diane | 2 |
| Gwen | 3 |
| Harold | 2 |
+--------+----------+统计每种动物的数量：
mysql> SELECT species, COUNT(*) FROM pet GROUP BY species;
+---------+----------+
| species | COUNT(*) |
+---------+----------+
| bird | 2 |
| cat | 2 |
| dog | 3 |
| hamster | 1 |
| snake | 1 |统计物种性别：
mysql> SELECT sex, COUNT(*) FROM pet GROUP BY sex;
+------+----------+
| sex | COUNT(*) |
+------+----------+
| NULL | 1 |
| f | 4 |
| m | 4 |
+------+----------+物种和性别的组合：
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 |
+---------+------+----------+只针对某个字段筛选，不用筛选整行
选择cat 和 dog种类，按照性别物种组合
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 |
+---------+------+----------+列出已知动物性别：
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 |
+---------+------+----------+mysql> SET sql_mode = ‘ONLY_FULL_GROUP_BY‘;-- 启用mysql> SELECT owner, COUNT(*) FROM pet;
ERROR 1140 (42000):ONLY_FULL_GROUP_BY 关闭后，结果不确定，系统随意添加一个值，最好关闭
mysql> SET sql_mode = ‘‘; -- 关闭
Query OK, 0 rows affected (0.00 sec)
mysql> SELECT owner, COUNT(*) FROM pet;
+--------+----------+
| owner | COUNT(*) |
+--------+----------+
| Harold | 9 |
+--------+----------+
mysql> SELECT owner, COUNT(*) FROM pet GROUP BY owner;
+--------+----------+
| owner | COUNT(*) |
+--------+----------+
| Benny | 2 |
| Diane | 2 |
| Gwen | 3 |
| Harold | 2 |
+--------+----------+3.4.9 使用多个表
此表格跟踪记录你的宠物，当你想记录他们的信息，比如看兽医、生幼崽、买玩具等事件，就需要另外一个表单记录，需要如下信息：
- 宠物名称：name
- 事件日期：date
- 事件类型：type
- 事件描述：emark
创建表一个符合上述要素的表单:
mysql> CREATE TABLE event (name VARCHAR(20), date DATE,
-> type VARCHAR(15), remark VARCHAR(255));将下述内容存储为event.txt
| name | date | type | remark |
|---|---|---|---|
| Fluffy | 1995-05-15 | litter | 4 kittens, 3 female, 1 male |
| Buffy | 1993-06-23 | litter | 5 puppies, 2 female, 3 male |
| Buffy | 1994-06-19 | litter | 3 puppies, 3 female |
| Chirpy | 1999-03-21 | vet | needed beak straightened |
| Slim | 1997-08-03 | vet | broken rib |
| Bowser | 1991-10-12 | kennel | |
| Fang | 1991-10-12 | kennel | |
| Fang | 1998-08-28 | birthday | Gave him a new chew toy |
| Claws | 1998-03-17 | birthday | Gave him a new flea collar |
| Whistler | 1998-12-09 | birthday | First birthday |
导入内容到表单
mysql> LOAD DATA LOCAL INFILE ‘event.txt‘ INTO TABLE event;假设：想知道每个宠物下崽时的年龄，宠物妈妈下崽时间在event表单，但是，出生日期在pet表单，所以要同时查询2个表单。
mysql> SELECT pet.name,
-> TIMESTAMPDIFF(YEAR,birth,date) 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
| 5 | 3 puppies, 3 female
+--------+------+------------------------------+jion表单:
- 是为从两张表获取信息
- 需要指定匹配规则，上述例子都有‘name‘
- 需要指定前缀
ON pet.name = event.name
表的自身连接
宠物的雌雄配对：
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 |
+--------+------+--------+------+---------+3.4 获取数据库和表的信息
查看目前使用的数据库
mysql> SELECT DATABASE();
+------------+
| DATABASE() |
+------------+
| menagerie |
+------------+查看表
mysql> SHOW TABLES;
+---------------------+
| Tables_in_menagerie |
+---------------------+
| event |
| pet |
+---------------------+查看表结构
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 | |
+---------+-------------+------+-----+---------+-------+3.5 批处理模式
在mysql内运行脚本：
mysql> source filename;
mysql> . filename来源：MySQL官网
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