初识MySQL

#Terminal中输入命令，等待下载安装完成，时间较长
$ brew install mysql
#若已安装则出现以下警告，安装操作随即停止
Warning: mysql 5.7.18_1 is already installed

$ sudo rm /usr/local/mysql
$ sudo rm -rf /usr/local/var/mysql
$ sudo rm -rf /usr/local/mysql*
$ sudo rm -rf /Library/Startupltens/MySQLCOM
$ sudo rm -rf /Library/PreferencePanes/My*
$ vim /etc/hostconfig and removed the line MYSQLCOM=-YES-rm -rf ~/Library/PreferencePanes/My*
$ sudo rm -rf /Library/Receipts/mysql*
$ sudo rm -rf /Library/Receipts/MySQL*
$ sudo rm -rf /var/db/receipts/com.mysql.*

# 启动MySQL
$ mysql.server start
Starting MySQL
. SUCCESS! 
# 建立本地连接并登录
$ mysql -u root -p
Enter password:      
#未改密码，默认为空，以下为登录后显示的信息 
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 4
Server version: 5.7.18 Homebrew

Copyright (c) 2000, 2017, 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.

# 查看MySQL基本信息
mysql> \s
--------------
mysql  Ver 14.14 Distrib 5.7.18, for osx10.12 (x86_64) using  EditLine wrapper

Connection id:        4
Current database:    
Current user:        root@localhost
SSL:            Not in use
Current pager:        stdout
Using outfile:        ''
Using delimiter:    ;
Server version:        5.7.18 Homebrew
Protocol version:    10
Connection:        Localhost via UNIX socket
Server characterset:    utf8
Db     charactersiet:    utf8
Client characterset:    utf8
Conn.  characterset:    utf8
UNIX socket:        /tmp/mysql.sock
Uptime:            32 sec

Threads: 1  Questions: 6  Slow queries: 0  Opens: 105  Flush tables: 1  Open tables: 98  Queries per second avg: 0.187
--------------

# 命令大小写均可用，但不知格式有无要求
# 显示数据库
mysql> SHOW DATABASES ;   
+--------------------+
| Database           |
+--------------------+
| information_schema |
| mysql              |
| performance_schema |
| sys                |
+--------------------+
4 rows in set (0.00 sec)


# 创建数据库mytest
mysql> CREATE DATABASE mytest;
Query OK, 1 row affected (0.01 sec)

# 检查数据库是否创建成功
mysql> SHOW DATABASES;
+--------------------+
| Database           |
+--------------------+
| information_schema |
| mysql              |
| mytest             |
| performance_schema |
| sys                |
+--------------------+
5 rows in set (0.00 sec)

# 未选择数据库情况，创建列表情况
mysql> CREATE TABLE employees (
    -> empid int not null,
    -> lastname varchar(30),
    -> firstname varchar(30),
    -> salary float,
    -> primary key (empid));
ERROR 1046 (3D000): No database selected

# 选择使用的数据库
mysql> USE mytest;
Database changed
mysql> SHOW tables;
Empty set (0.00 sec)
#在mytest数据库中创建employees表
mysql> create table employees (
    -> empid int not null,
    -> lastname varchar(30),
    -> firstname varchar(30),
    -> salary float,
    -> primary key (empid));
Query OK, 0 rows affected (0.03 sec)

# empid数据字段还指定了一个数据约束 (data constraint)。数据约束会限制输入什么类型数据可以创建一个有效的记录。
# not null数据指明每条记录都必须有一个指定的empid值。
# 最后，primary key定义了可以唯一标识每条记录的数据字段。这意味着每条记录中在表中都必须有一个唯一的empid值。

#查看是否创建成功
mysql> show tables;
+------------------+
| Tables_in_mytest |
+------------------+
| employees        |
+------------------+
1 row in set (0.00 sec)

#插入记录，格式：INSERT INTO table VALUES (....)

mysql> INSERT INTO employees VALUES (1, 'Blum', 'Rich', 2500.00);
Query OK, 1 row affected (0.01 sec)

#插入相同记录会出现错误提示
mysql> INSERT INTO employees VALUES (1, 'Blum', 'Rich', 2500.00);
ERROR 1062 (23000): Duplicate entry '1' for key 'PRIMARY'

#删除指定记录，格式：DELETE FROM employees WHERE enpid = 2;
mysql> DELETE FROM employees WHERE empid = 1;
Query OK, 1 row affected (0.00 sec)

mysql> INSERT INTO employees VALUES (2, 'Blum', 'Barbara', 45000.00);
Query OK, 1 row affected (0.00 sec)

mysql> INSERT INTO employees VALUES (1, 'Blum', 'Rich', 25000.00);
Query OK, 1 row affected (0.00 sec)

mysql> INSERT INTO employees VALUES (3, 'Blum', 'Katie Jane', 34500.00);
Query OK, 1 row affected (0.00 sec)

mysql> INSERT INTO employees VALUES (4, 'Blum', 'Jessica', 52340.00);
Query OK, 1 row affected (0.00 sec)

#查询数据，格式：SELECT datafields FROM table；datafields参数是一个用逗号分开的数据字段名称列表，
#指明了希望查询返回的字段。如果你要提取所有的数据字段值，可以用星号作通配符。
#查询所有记录

mysql> SELECT * FROM employees;
+-------+----------+------------+--------+
| empid | lastname | firstname  | salary |
+-------+----------+------------+--------+
|     1 | Blum     | Rich       |  25000 |
|     2 | Blum     | Barbara    |  45000 |
|     3 | Blum     | Katie Jane |  34500 |
|     4 | Blum     | Jessica    |  52340 |
+-------+----------+------------+--------+
4 rows in set (0.00 sec)

#常用的修修饰符。
#  WHERE:显示符合特定条件的数据行子集。
#  ORDER BY:以指定顺序显示数据行。
#  LIMIT:只显示数据行的一个子集。

mysql> SELECT * FROM employees WHERE salary > 40000;
+-------+----------+-----------+--------+
| empid | lastname | firstname | salary |
+-------+----------+-----------+--------+
|     2 | Blum     | Barbara   |  45000 |
|     4 | Blum     | Jessica   |  52340 |
+-------+----------+-----------+--------+
2 rows in set (0.00 sec)

#退出
mysql> exit
Bye

#关闭数据库连接
$ mysql.server stop
Shutting down MySQL
.. SUCCESS!