mysql8.0.16操作记录
2.1、登录
[root@db143 local]# mysql -h 127.0.0.1 -P 3306 -uroot -p'AnvcTMagdLarwNV3CKaC'
mysql: [Warning] Using a password on the command line interface can be insecure.
Welcome to the MySQL monitor. Commands end with ; or g.
Your MySQL connection id is 18
Server version: 8.0.16 MySQL Community Server - GPL
Copyright (c) 2000, 2019, Oracle and/or its affiliates. All rights reserved.
Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.
Type 'help;' or 'h' for help. Type 'c' to clear the current input statement.
2.2、创建数据库
mysql> create database company;
Query OK, 1 row affected (0.00 sec)
mysql> show create database company;
+----------+-----------------------------------------------------------------------------------------------------------------------------------+
| Database | Create Database |
+----------+-----------------------------------------------------------------------------------------------------------------------------------+
| company | CREATE DATABASE `company` /*!40100 DEFAULT CHARACTER SET utf8mb4 COLLATE utf8mb4_0900_ai_ci */ /*!80016 DEFAULT ENCRYPTION='N' */ |
+----------+-----------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)
-- 含有特殊字符的，需要用反引号转义
mysql> create database `my.contacts`;
Query OK, 1 row affected (0.01 sec)
mysql> show create database `my.contacts`;
+-------------+---------------------------------------------------------------------------------------------------------------------------------------+
| Database | Create Database |
+-------------+---------------------------------------------------------------------------------------------------------------------------------------+
| my.contacts | CREATE DATABASE `my.contacts` /*!40100 DEFAULT CHARACTER SET utf8mb4 COLLATE utf8mb4_0900_ai_ci */ /*!80016 DEFAULT ENCRYPTION='N' */ |
+-------------+---------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)
mysql>
2.3、直接连接库
[root@db143 local]# mysql -h 127.0.0.1 -P 3306 -uroot -p'AnvcTMagdLarwNV3CKaC' company
mysql: [Warning] Using a password on the command line interface can be insecure.
Welcome to the MySQL monitor. Commands end with ; or g.
Your MySQL connection id is 19
Server version: 8.0.16 MySQL Community Server - GPL
Copyright (c) 2000, 2019, Oracle and/or its affiliates. All rights reserved.
Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.
Type 'help;' or 'h' for help. Type 'c' to clear the current input statement.
mysql> select database();
+------------+
| database() |
+------------+
| company |
+------------+
1 row in set (0.00 sec)
mysql>
mysql> show databases;
+--------------------+
| Database |
+--------------------+
| company |
| information_schema |
| my.contacts |
| mysql |
| performance_schema |
| sys |
+--------------------+
6 rows in set (0.00 sec)
2.4、查看数据目录
mysql> show variables like 'datadir';
+---------------+------------------------------+
| Variable_name | Value |
+---------------+------------------------------+
| datadir | /data/mysql/mysql_3306/data/ |
+---------------+------------------------------+
1 row in set (0.00 sec)
mysql> #
-- 检查对应的物理文件
[root@db143 ~]# ll /data/mysql/mysql_3306/data/
total 7375972
-rw-r-----. 1 mysql mysql 56 Apr 18 00:52 auto.cnf
-rw-------. 1 mysql mysql 1676 Apr 18 00:52 ca-key.pem
-rw-r--r--. 1 mysql mysql 1112 Apr 18 00:52 ca.pem
-rw-r--r--. 1 mysql mysql 1112 Apr 18 00:52 client-cert.pem
-rw-------. 1 mysql mysql 1680 Apr 18 00:52 client-key.pem
drwxr-x---. 2 mysql mysql 4096 Apr 18 01:01 company
-rw-r-----. 1 mysql mysql 5452 Apr 18 00:52 ib_buffer_pool
-rw-r-----. 1 mysql mysql 1073741824 Apr 18 01:03 ibdata1
-rw-r-----. 1 mysql mysql 2147483648 Apr 18 01:03 ib_logfile0
-rw-r-----. 1 mysql mysql 2147483648 Apr 18 00:52 ib_logfile1
-rw-r-----. 1 mysql mysql 2147483648 Apr 18 00:52 ib_logfile2
-rw-r-----. 1 mysql mysql 12582912 Apr 18 00:53 ibtmp1
-rw-r-----. 1 mysql mysql 6960 Apr 18 01:05 innodb_status.3236
drwxr-x---. 2 mysql mysql 4096 Apr 18 00:53 #innodb_temp
drwxr-x---. 2 mysql mysql 4096 Apr 18 01:02 my@002econtacts
drwxr-x---. 2 mysql mysql 4096 Apr 18 00:52 mysql
-rw-r-----. 1 mysql mysql 5 Apr 18 00:53 mysql_3306.pid
-rw-r-----. 1 mysql mysql 24117248 Apr 18 01:03 mysql.ibd
drwxr-x---. 2 mysql mysql 4096 Apr 18 00:52 performance_schema
-rw-------. 1 mysql mysql 1676 Apr 18 00:52 private_key.pem
-rw-r--r--. 1 mysql mysql 452 Apr 18 00:52 public_key.pem
-rw-r--r--. 1 mysql mysql 1112 Apr 18 00:52 server-cert.pem
-rw-------. 1 mysql mysql 1680 Apr 18 00:52 server-key.pem
drwxr-x---. 2 mysql mysql 4096 Apr 18 00:52 sys
[root@db143 ~]#
2.4.1、创建表
CREATE TABLE IF NOT EXISTS `company`.`customers`(
id int unsigned NOT NULL AUTO_INCREMENT PRIMARY KEY,
first_name varchar(20) NOT NULL COMMENT 'first_name',
last_name varchar(20) NOT NULL COMMENT 'last_name',
country varchar(20) NOT NULL COMMENT '国家'
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4;
mysql> show create table customersG;
*************************** 1. row ***************************
Table: customers
Create Table: CREATE TABLE `customers` (
`id` int(10) unsigned NOT NULL AUTO_INCREMENT,
`first_name` varchar(20) NOT NULL COMMENT 'first_name',
`last_name` varchar(20) NOT NULL COMMENT 'last_name',
`country` varchar(20) NOT NULL COMMENT '国家',
PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_0900_ai_ci
1 row in set (0.00 sec)
ERROR:
No query specified
-- 列出所有的存储引擎
mysql> show engines;
+--------------------+---------+----------------------------------------------------------------+--------------+------+------------+
| Engine | Support | Comment | Transactions | XA | Savepoints |
+--------------------+---------+----------------------------------------------------------------+--------------+------+------------+
| FEDERATED | NO | Federated MySQL storage engine | NULL | NULL | NULL |
| MEMORY | YES | Hash based, stored in memory, useful for temporary tables | NO | NO | NO |
| InnoDB | DEFAULT | Supports transactions, row-level locking, and foreign keys | YES | YES | YES |
| PERFORMANCE_SCHEMA | YES | Performance Schema | NO | NO | NO |
| MyISAM | YES | MyISAM storage engine | NO | NO | NO |
| MRG_MYISAM | YES | Collection of identical MyISAM tables | NO | NO | NO |
| BLACKHOLE | YES | /dev/null storage engine (anything you write to it disappears) | NO | NO | NO |
| CSV | YES | CSV storage engine | NO | NO | NO |
| ARCHIVE | YES | Archive storage engine | NO | NO | NO |
+--------------------+---------+----------------------------------------------------------------+--------------+------+------------+
9 rows in set (0.00 sec)
mysql> CREATE TABLE payment(
id int(10) unsigned NOT NULL AUTO_INCREMENT,
customer_name varchar(20) NOT NULL COMMENT '客户名称',
payment_num decimal(10,2) NOT NULL DEFAULT '0.00' COMMENT '金额',
PRIMARY KEY(id)
)ENGINE=InnoDB DEFAULT CHARSET=utf8mb4;
mysql> show create table paymentG;
*************************** 1. row ***************************
Table: payment
Create Table: CREATE TABLE `payment` (
`id` int(10) unsigned NOT NULL AUTO_INCREMENT,
`customer_name` varchar(20) NOT NULL COMMENT '客户名称',
`payment_num` decimal(10,2) NOT NULL DEFAULT '0.00' COMMENT '金额',
PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_0900_ai_ci
1 row in set (0.00 sec)
ERROR:
No query specified
mysql> show tables;
+-------------------+
| Tables_in_company |
+-------------------+
| customers |
| payment |
+-------------------+
2 rows in set (0.01 sec)
mysql>
2.4.2、查看目录
[root@db143 ~]# ll /data/mysql/mysql_3306/data/company/
total 164
-rw-r-----. 1 mysql mysql 114688 Apr 18 01:21 customers.ibd
-rw-r-----. 1 mysql mysql 114688 Apr 18 01:32 payment.ibd
[root@db143 ~]#
2.4.3、克隆表
mysql> CREATE TABLE new_customers LIKE customers;
Query OK, 0 rows affected (0.10 sec)
mysql> show create table new_customersG
*************************** 1. row ***************************
Table: new_customers
Create Table: CREATE TABLE `new_customers` (
`id` int(10) unsigned NOT NULL AUTO_INCREMENT,
`first_name` varchar(20) NOT NULL COMMENT 'first_name',
`last_name` varchar(20) NOT NULL COMMENT 'last_name',
`country` varchar(20) NOT NULL COMMENT '国家',
PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_0900_ai_ci
1 row in set (0.01 sec)
2.5、插入、更新和删除行
INSERT、UPDATE、DELETE和SELECT操作成为数据操作语言(DML)语句。
2.5.1、插入操作
*/
INSERT IGNORE INTO customers (first_name,last_name,country)
VALUES
('Mike','Christensen','USA'),
('Andy','Hollands','Astralia'),
('Ravi','Vendantam','India'),
('Rajiv','Perera','Sri Lanka');
-- 或者
INSERT IGNORE INTO customers (id,first_name,last_name,country)
VALUES
(1,'Mike','Christensen','USA'),
(2,'Andy','Hollands','Astralia'),
(3,'Ravi','Vendantam','India'),
(4,'Rajiv','Perera','Sri Lanka');
/*
IGNORE：如果该行已经存在，并给出了IGNORE子句，则新数据将被忽略，
INSERT语句仍然会执行成功，同时生成一个告警信息和重复数据的数目。
反之，如果未给出IGNORE子句，则INSERT语句会生成一条错误信息。
*/
mysql> show warnings;
+---------+------+---------------------------------------+
| Level | Code | Message |
+---------+------+---------------------------------------+
| Warning | 1062 | Duplicate entry '1' for key 'PRIMARY' |
| Warning | 1062 | Duplicate entry '2' for key 'PRIMARY' |
| Warning | 1062 | Duplicate entry '3' for key 'PRIMARY' |
| Warning | 1062 | Duplicate entry '4' for key 'PRIMARY' |
+---------+------+---------------------------------------+
4 rows in set (0.00 sec)
mysql>
-- 更新，UPDATE语句用来修改表中的现有记录。
mysql> select * from customers;
+----+------------+-------------+-----------+
| id | first_name | last_name | country |
+----+------------+-------------+-----------+
| 1 | Mike | Christensen | USA |
| 2 | Andy | Hollands | Astralia |
| 3 | Ravi | Vendantam | India |
| 4 | Rajiv | Perera | Sri Lanka |
+----+------------+-------------+-----------+
4 rows in set (0.00 sec)
mysql> UPDATE customers SET first_name='Rajiver',country='UK' WHERE id=4;
Query OK, 1 row affected (0.05 sec)
Rows matched: 1 Changed: 1 Warnings: 0
mysql> select * from customers;
+----+------------+-------------+----------+
| id | first_name | last_name | country |
+----+------------+-------------+----------+
| 1 | Mike | Christensen | USA |
| 2 | Andy | Hollands | Astralia |
| 3 | Ravi | Vendantam | India |
| 4 | Rajiver | Perera | UK |
+----+------------+-------------+----------+
4 rows in set (0.00 sec)
mysql>
-- 删除，DELETE用来删除数据
mysql> DELETE FROM customers WHERE id=4 AND first_name='Rajiver';
Query OK, 1 row affected (0.36 sec)
mysql> select * from customers;
+----+------------+-------------+----------+
| id | first_name | last_name | country |
+----+------------+-------------+----------+
| 1 | Mike | Christensen | USA |
| 2 | Andy | Hollands | Astralia |
| 3 | Ravi | Vendantam | India |
+----+------------+-------------+----------+
3 rows in set (0.00 sec)
mysql>
/*
REPLACE、INSERT 、ON DUPLICATE KEY UPDATE
在很多情况下，我们需要处理重复的数据。行的唯一性由主键标识。如果行已经存在，
则REPLACE会简单的删除行并插入新行；如果行不存在，则REPLACE等同于INSERT。
*/
REPLACE INTO customers VALUES (1,'Mike','Christensen','Amercia');
mysql> SELECT * FROM customers;
+----+------------+-------------+-----------+
| id | first_name | last_name | country |
+----+------------+-------------+-----------+
| 1 | Mike | Christensen | USA |
| 2 | Andy | Hollands | Astralia |
| 3 | Ravi | Vendantam | India |
| 4 | Rajiv | Perera | Sri Lanka |
+----+------------+-------------+-----------+
4 rows in set (0.00 sec)
mysql> REPLACE INTO customers VALUES (1,'Mike','Christensen','Amercia');
Query OK, 2 rows affected (0.00 sec)
-- 可以看到有两行受到影响，一个重复行被删除，一个新行被插入
mysql> SELECT * FROM customers;
+----+------------+-------------+-----------+
| id | first_name | last_name | country |
+----+------------+-------------+-----------+
| 1 | Mike | Christensen | Amercia |
| 2 | Andy | Hollands | Astralia |
| 3 | Ravi | Vendantam | India |
| 4 | Rajiv | Perera | Sri Lanka |
+----+------------+-------------+-----------+
4 rows in set (0.00 sec)
mysql>
mysql> INSERT INTO payment(customer_name,payment_num) VALUES('Mike Christensen',200) ON DUPLICATE KEY UPDATE payment_num=payment_num+VALUES(payment_num);
Query OK, 1 row affected (0.01 sec)
mysql> INSERT INTO payment(customer_name,payment_num) VALUES('Rajiv Perera',500) ON DUPLICATE KEY UPDATE payment_num=payment_num+VALUES(payment_num);
Query OK, 1 row affected (0.01 sec)
mysql> select * from payment;
+----+------------------+-------------+
| id | customer_name | payment_num |
+----+------------------+-------------+
| 1 | Mike Christensen | 200.00 |
| 2 | Rajiv Perera | 500.00 |
+----+------------------+-------------+
2 rows in set (0.00 sec)
-- 当Mike Christensen下次支付300美元时，将更新该行并将此付款金额添加到以前的金额中
mysql> INSERT INTO payment(id,customer_name,payment_num) VALUES(1,'Mike Christensen',500) ON DUPLICATE KEY UPDATE payment_num=payment_num+VALUES(payment_num);
Query OK, 2 rows affected (0.00 sec)
mysql> select * from payment;
+----+------------------+-------------+
| id | customer_name | payment_num |
+----+------------------+-------------+
| 1 | Mike Christensen | 700.00 |
| 2 | Rajiv Perera | 500.00 |
+----+------------------+-------------+
2 rows in set (0.00 sec)
2.6、截断表
mysql> truncate table customers;
Query OK, 0 rows affected (0.09 sec)
2.7、下载安装示例数据库
下载示例数据
https://codeload.github.com/datacharmer/test_db/zip/master
cd /opt/
wget 'https://codeload.github.com/datacharmer/test_db/zip/master' -O master.zip
unzip master.zip
cd /opt/test_db-master
[root@db143 test_db-master]# mysql.3306.login < /opt/test_db-master/employees.sql
mysql: [Warning] Using a password on the command line interface can be insecure.
INFO
CREATING DATABASE STRUCTURE
INFO
storage engine: InnoDB
INFO
LOADING departments
INFO
LOADING employees
INFO
LOADING dept_emp
INFO
LOADING dept_manager
INFO
LOADING titles
INFO
LOADING salaries
data_load_time_diff
00:01:05
[root@db143 test_db-master]#
[root@db143 test_db-master]# mysql.3306.login employees -A
mysql: [Warning] Using a password on the command line interface can be insecure.
Welcome to the MySQL monitor. Commands end with ; or g.
Your MySQL connection id is 24
Server version: 8.0.16 MySQL Community Server - GPL
Copyright (c) 2000, 2019, Oracle and/or its affiliates. All rights reserved.
Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.
Type 'help;' or 'h' for help. Type 'c' to clear the current input statement.
mysql> show tables;
+----------------------+
| Tables_in_employees |
+----------------------+
| current_dept_emp |
| departments |
| dept_emp |
| dept_emp_latest_date |
| dept_manager |
| employees |
| salaries |
| titles |
+----------------------+
8 rows in set (0.10 sec)
mysql>
mysql> show create table employeesG;
*************************** 1. row ***************************
Table: employees
Create Table: CREATE TABLE `employees` (
`emp_no` int(11) NOT NULL,
`birth_date` date NOT NULL,
`first_name` varchar(14) NOT NULL,
`last_name` varchar(16) NOT NULL,
`gender` enum('M','F') NOT NULL,
`hire_date` date NOT NULL,
PRIMARY KEY (`emp_no`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_0900_ai_ci
1 row in set (0.35 sec)
ERROR:
No query specified
mysql>
2.7.1、如何操作
mysql> select * from departments;
+---------+--------------------+
| dept_no | dept_name |
+---------+--------------------+
| d009 | Customer Service |
| d005 | Development |
| d002 | Finance |
| d003 | Human Resources |
| d001 | Marketing |
| d004 | Production |
| d006 | Quality Management |
| d008 | Research |
| d007 | Sales |
+---------+--------------------+
9 rows in set (0.10 sec)
mysql>
-- 选择列
mysql> select dept_no,emp_no from dept_manager;
+---------+--------+
| dept_no | emp_no |
+---------+--------+
| d001 | 110022 |
| d001 | 110039 |
| d002 | 110085 |
| d002 | 110114 |
| d003 | 110183 |
| d003 | 110228 |
| d004 | 110303 |
| d004 | 110344 |
| d004 | 110386 |
| d004 | 110420 |
| d005 | 110511 |
| d005 | 110567 |
| d006 | 110725 |
| d006 | 110765 |
| d006 | 110800 |
| d006 | 110854 |
| d007 | 111035 |
| d007 | 111133 |
| d008 | 111400 |
| d008 | 111534 |
| d009 | 111692 |
| d009 | 111784 |
| d009 | 111877 |
| d009 | 111939 |
+---------+--------+
24 rows in set (0.05 sec)
2.7.2、计数
mysql> select count(*) from employees;
+----------+
| count(*) |
+----------+
| 300024 |
+----------+
1 row in set (1.53 sec)
mysql> select emp_no from employees where first_name='Georgi' and last_name='Facello' ;
+--------+
| emp_no |
+--------+
| 10001 |
| 55649 |
+--------+
2 rows in set (0.10 sec)
-- 找出姓氏为Christ、Lamba或者Baba的所有员工的人数
mysql> select count(*) from employees where first_name in ('Christ','Lamba','Baba') ;
+----------+
| count(*) |
+----------+
| 238 |
+----------+
1 row in set (0.09 sec)
-- 找出1986年12月入职的员工人数
mysql> select count(*) from employees where hire_date between '1986-12-01' and '1986-12-31';
+----------+
| count(*) |
+----------+
| 3081 |
+----------+
1 row in set (0.08 sec)
mysql> select count(*) from employees where hire_date not between '1986-12-01' and '1986-12-31';
+----------+
| count(*) |
+----------+
| 296943 |
+----------+
1 row in set (0.08 sec)
-- 找出名字以Christ开头的所有员工的人数
mysql> select count(*) from employees where first_name like 'Christ%';
+----------+
| count(*) |
+----------+
| 1157 |
+----------+
1 row in set (0.07 sec)
mysql>
-- 找出名字以Christ开头并以ed结尾的所有员工的人数
mysql> select count(*) from employees where first_name like 'Christ%ed';
+----------+
| count(*) |
+----------+
| 228 |
+----------+
1 row in set (0.07 sec)
mysql>
-- 找出名字中包含sri所有员工的人数
mysql> select count(*) from employees where first_name like '%sri%';
+----------+
| count(*) |
+----------+
| 253 |
+----------+
1 row in set (0.11 sec)
-- 找到名字以er结尾的所有员工的人数
mysql> select count(*) from employees where first_name like '%ed';
+----------+
| count(*) |
+----------+
| 1181 |
+----------+
1 row in set (0.09 sec)
-- 找出名字以任意两个字符开头、后面跟随ka、再后面跟随任意数量字符的所有员工的人数
mysql> select count(*) from employees where first_name like '__ka%';
+----------+
| count(*) |
+----------+
| 1918 |
+----------+
1 row in set (0.08 sec)
2.7.3、正则表达式
正则表达式
表达式 描述
* 零次或多次重复
+ 一个或多个重复
？ 可选字符
. 任何字符
. 区间
^ 以......开始
$ 以......结尾
[abc] 只有a、b或者c
[^abc] 非a、非b,亦非c
[a-z] 字符a到z
[0-9] 数字0-9
^...$ 开始和结束
d 任何数字
D 任何非数字字符
s 任何空格
S 任何非空格
w 任何字母数字字符
W 任何非字母数字字符
{m} m次重复
{m,n} m到n次重复
-- 找出名字以Christ开头的所有员工的人数
mysql> select count(*) from employees where last_name regexp '^Christ';
+----------+
| count(*) |
+----------+
| 373 |
+----------+
1 row in set (0.22 sec)
mysql> select count(*) from employees where last_name rlike '^Christ';
+----------+
| count(*) |
+----------+
| 373 |
+----------+
1 row in set (0.23 sec)
-- 找出姓氏以ba结尾的所有员工人数
mysql> select count(*) from employees where last_name regexp 'ba$';
+----------+
| count(*) |
+----------+
| 1008 |
+----------+
1 row in set (0.20 sec)
mysql>
-- 查找姓氏不包含元音字母(a,e,i,o,u)的所有员工的人数
mysql> select count(*) from employees where last_name not regexp '[aeiou]';
+----------+
| count(*) |
+----------+
| 148 |
+----------+
1 row in set (0.23 sec)
mysql>
-- 查询hire_date在1986年之前的任何10名员工的姓名
mysql> select first_name,last_name from employees where hire_date < '1986-01-01' limit 10;
+------------+------------+
| first_name | last_name |
+------------+------------+
| Bezalel | Simmel |
| Sumant | Peac |
| Eberhardt | Terkki |
| Otmar | Herbst |
| Florian | Syrotiuk |
| Tse | Herber |
| Udi | Jansch |
| Reuven | Garigliano |
| Erez | Ritzmann |
| Premal | Baek |
+------------+------------+
10 rows in set (0.05 sec)
mysql>
-- 使用表别名
mysql> select count(*) AS count from employees where hire_date between '1986-12-01' and '1986-12-31';
+-------+
| count |
+-------+
| 3081 |
+-------+
1 row in set (0.08 sec)
mysql>
2.8、对结果进行排序
-- 查找薪水最高的前5名员工的员工编号
mysql> select emp_no,salary from salaries order by salary desc limit 5;
+--------+--------+
| emp_no | salary |
+--------+--------+
| 43624 | 158220 |
| 43624 | 157821 |
| 254466 | 156286 |
| 47978 | 155709 |
| 253939 | 155513 |
+--------+--------+
5 rows in set (0.96 sec)
2.9、对结果分组
-- count 1 分别找出男性和女性员工的人数
mysql> select count(*),gender from employees group by gender;
+----------+--------+
| count(*) | gender |
+----------+--------+
| 179973 | M |
| 120051 | F |
+----------+--------+
2 rows in set (0.17 sec)
-- 2 如果希望查找员工名字中最常见的10个名字，可以使用group by(first_name),对名字进行
-- 分组，然后使用count(first_name)在各组内计数，最后使用order by 计数对结果进行排序
mysql> select count(first_name) AS COUNT, first_name from employees group by first_name order by count desc limit 10;
+-------+-------------+
| COUNT | first_name |
+-------+-------------+
| 295 | Shahab |
| 291 | Tetsushi |
| 279 | Elgin |
| 278 | Anyuan |
| 276 | Huican |
| 275 | Make |
| 272 | Sreekrishna |
| 272 | Panayotis |
| 271 | Hatem |
| 270 | Shen |
+-------+-------------+
10 rows in set (0.29 sec)
-- sum 查找每年给与员工的薪水总额，并按照薪水的高低对结果进行排序。year()函数将返回给定日期所在的年份
mysql> select '2017-06-12', year('2017-06-12');
+------------+--------------------+
| 2017-06-12 | year('2017-06-12') |
+------------+--------------------+
| 2017-06-12 | 2017 |
+------------+--------------------+
1 row in set (0.00 sec)
mysql> select '2017-06-12', month('2017-06-12');
+------------+---------------------+
| 2017-06-12 | month('2017-06-12') |
+------------+---------------------+
| 2017-06-12 | 6 |
+------------+---------------------+
1 row in set (0.00 sec)
mysql> select '2017-06-12', day('2017-06-12');
+------------+-------------------+
| 2017-06-12 | day('2017-06-12') |
+------------+-------------------+
| 2017-06-12 | 12 |
+------------+-------------------+
1 row in set (0.00 sec)
mysql> select year(from_date) AS year_s,sum(salary) AS SUM from salaries group by year_s order by sum desc ;
+--------+-------------+
| year_s | SUM |
+--------+-------------+
| 2000 | 17535667603 |
| 2001 | 17507737308 |
| 1999 | 17360258862 |
| 1998 | 16220495471 |
| 1997 | 15056011781 |
| 1996 | 13888587737 |
| 1995 | 12638817464 |
| 1994 | 11429450113 |
| 2002 | 10243347616 |
| 1993 | 10215059054 |
| 1992 | 9027872610 |
| 1991 | 7798804412 |
| 1990 | 6626146391 |
| 1989 | 5454260439 |
| 1988 | 4295598688 |
| 1987 | 3156881054 |
| 1986 | 2052895941 |
| 1985 | 972864875 |
+--------+-------------+
18 rows in set (1.81 sec)
mysql>
-- 查找平均工资最高的前10名员工
select emp_no,avg(salary) AS avg FROM salaries group by emp_no order by avg desc limit 10;
mysql> select emp_no,avg(salary) AS avg FROM salaries group by emp_no order by avg desc limit 10;
+--------+-------------+
| emp_no | avg |
+--------+-------------+
| 109334 | 141835.3333 |
| 205000 | 141064.6364 |
| 43624 | 138492.9444 |
| 493158 | 138312.8750 |
| 37558 | 138215.8571 |
| 276633 | 136711.7333 |
| 238117 | 136026.2000 |
| 46439 | 135747.7333 |
| 254466 | 135541.0625 |
| 253939 | 135042.2500 |
+--------+-------------+
10 rows in set (0.95 sec)
-- distinct 使用distinct字句过滤出来表中的不同条目
mysql> select distinct title from titles;
+--------------------+
| title |
+--------------------+
| Senior Engineer |
| Staff |
| Engineer |
| Senior Staff |
| Assistant Engineer |
| Technique Leader |
| Manager |
+--------------------+
7 rows in set (1.79 sec)
-- 使用having过滤，找到平均工资超过140,000美元的员工
mysql> select emp_no,avg(salary) AS avg from salaries group by emp_no having avg > 140000 order by avg desc;
+--------+-------------+
| emp_no | avg |
+--------+-------------+
| 109334 | 141835.3333 |
| 205000 | 141064.6364 |
+--------+-------------+
2 rows in set (1.00 sec)