Database基礎(一):構建MySQL服務器、 數據庫基本管理 、MySQL 數據類型、表結構的調整

1、構建MySQL服務器html

目標:mysql

本案例要求熟悉MySQL官方安裝包的使用,快速構建一臺數據庫服務器:sql

  •     安裝MySQL-server、MySQl-client軟件包
  •     修改數據庫用戶root的密碼
  •     確認MySQL服務程序運行、root可控

方案:數據庫

本課程將使用64位的RHEL 7操做系統,MySQL數據庫的版本是5.7.17。bootstrap

訪問http://dev.mysql.com/downloads/mysql/,找到MySQL Community Server下載頁面,平臺選擇「Red Hat Enterprise Linux 7 / Oracle Linux」,而後選擇64位的bundle整合包下載,以下圖所示。vim

                         

注意:下載MySQL軟件時須要以Oracle網站帳戶登陸,若是沒有請根據頁面提示先註冊一個(免費) 。安全

步驟:服務器

步驟一:準備工做socket

1)卸載系統自帶的mariadb-server、mariadb軟件包(若是有的話)tcp

    [root@dbsvr1 ~]# yum -y remove mariadb-server mariadb
    Setting up Remove Process
    No Match for argument: mariadb-server
    rhel7dvd                                                 | 3.9 kB     00:00 ...
    Package(s) mariadb-server available, but not installed.
    No Match for argument: mariadb
    Package(s) mariadb available, but not installed.
    No Packages marked for removal

2)清理/etc/my.cnf配置文件

此配置文件由RHEL自帶的mariadb-libs庫提供:

    [root@dbsvr1 ~]# rpm -qf /etc/my.cnf
    mariadb-libs-5.5.35-3.el7.x86_64

大量的系統軟件包都須要用到mariadb-libs庫,所以不建議直接卸載此軟件包。最好是安裝新的MySQL數據庫軟件時,採用 -U 升級的方式來進行替換。

配置文件/etc/my.cnf若不須要使用,能夠直接刪除。或者保險起見,也能夠將其更名備份:

    [root@dbsvr1 ~]# mv /etc/my.cnf /etc/my.cnf.old

步驟二:安裝mysql-community-client、mysql-community-server軟件包

1)釋放bundle整合包

    [root@dbsvr1 ~]# cd /var/ftp/pub/
    [root@dbsvr1 pub]# tar xvf mysql-5.7.17-1.el7.x86_64.rpm-bundle.tar
    mysql-community-client-5.7.17-1.el7.x86_64.rpm                
    //MySQL 數據庫客戶端應用程序和工具
    mysql-community-common-5.7.17-1.el7.x86_64.rpm                 
    //MySQL 數據庫和客戶端庫共享文件
    mysql-community-devel-5.7.17-1.el7.x86_64.rpm                  
    //MySQL 數據庫客戶端應用程序的庫和頭文件
    mysql-community-embedded-5.7.17-1.el7.x86_64.rpm              
    //MySQL嵌入式函數庫
    mysql-community-embedded-compat-5.7.17-1.el7.x86_64.rpm
    //MySQL嵌入式兼容函數庫
    mysql-community-embedded-devel-5.7.17-1.el7.x86_64.rpm
    //頭文件和庫文件做爲Mysql的嵌入式庫文件
    mysql-community-libs-5.7.17-1.el7.x86_64.rpm
    //MySQL 數據庫客戶端應用程序的共享庫
    mysql-community-libs-compat-5.7.17-1.el7.x86_64.rpm
    //MySQL 5.6.31 數據庫客戶端應用程序的共享兼容庫
    mysql-community-minimal-debuginfo-5.7.17-1.el7.x86_64.rpm     
    //mysql最小安裝包的調試信息
    mysql-community-server-5.7.17-1.el7.x86_64.rpm
    //很是快速和可靠的 SQL 數據庫服務器
    mysql-community-server-minimal-5.7.17-1.el7.x86_64.rpm  
    //很是快速和可靠的 SQL 數據庫服務器(最小化安裝)
    mysql-community-test-5.7.17-1.el7.x86_64.rpm                   
    //MySQL 數據庫服務器的測試套件

2)安裝MySQL數據庫

在bundle的整合包中,並非全部的rpm包都會用到,將一些重複的刪除。

安裝mysql時可能會缺乏某些依賴包,需提早單獨安裝

    [root@dbsvr1 pub]#yum -y  install perl-Data-Dumper  perl-JSON  perl-Time-HiRes
    [root@dbsvr1 pub]# rpm -Uvh mysql-community-*.rpm
    準備中...                          ################################# [100%]
    正在升級/安裝...
       1:mysql-community-common-5.7.17-1.e################################# [  9%]
       2:mysql-community-libs-5.7.17-1.el7################################# [ 18%]
       3:mysql-community-client-5.7.17-1.e################################# [ 27%]
       4:mysql-community-server-5.7.17-1.e################################# [ 36%]
       5:mysql-community-devel-5.7.17-1.el################################# [ 45%]
       6:mysql-community-embedded-5.7.17-1################################# [ 55%]
       7:mysql-community-embedded-devel-5.################################# [ 64%]
       8:mysql-community-test-5.7.17-1.el7################################# [ 73%]
       9:mysql-community-libs-compat-5.7.1################################# [ 82%]
      10:mysql-community-minimal-debuginfo################################# [ 91%]
    正在清理/刪除...
      11:mariadb-libs-1:5.5.35-3.el7      ################################# [100%]
    [root@dbsvr1 pub]#systemctl start mysqld.service

安裝過程當中會嘗試作一些檢測,而後完成基本的初始化任務,期間會給出相關的提示。好比因爲MySQL 5.7對TIMESTAMP時間戳的處理不一樣於以前的版本,會給出警告和提示出解決辦法(使用 --explicit_defaults_for_timestamp選項):

    2017-04-04T15:59:07.324470Z 0 [Warning] TIMESTAMP with implicit DEFAULT value is deprecated. Please use --explicit_defaults_for_timestamp server option (see documentation for more details).

MySQL 5.7默認採用的存儲引擎再也不是MyISAM,而是InnoDB。初始化時若相關的文件不存在,會自動建立並設置相關參數:

    2017-04-04T15:59:09.075698Z 0 [Warning] InnoDB: New log files created, LSN=45790
    2017-04-04T15:59:09.381634Z 0 [Warning] InnoDB: Creating foreign key constraint system tables.
    2017-04-04T15:59:09.579733Z 0 [Warning] No existing UUID has been found, so we assume that this is the first time that this server has been started. Generating a new UUID: a3973917-194f-11e7-a75b-52540018542e.
    2017-04-04T15:59:09.703759Z 0 [Warning] Gtid table is not ready to be used. Table 'mysql.gtid_executed' cannot be opened.
    2017-04-04T15:59:09.711439Z 1 [Note] A temporary password is generated for root@localhost: ;%7SDdD)quOI
    2017-04-04T15:59:29.758102Z 1 [ERROR] Failed to open the bootstrap file /tmp/install-validate-password-plugin.xqy7Ay.sql
    2017-04-04T15:59:29.758122Z 1 [ERROR] 1105  Bootstrap file error, return code (0). Nearest query: 'LSE SET @sys.tmp.table_exists.SQL = CONCAT('SELECT COUNT(*) FROM `', in_db, '`.`', in_table, '`'); PREPARE stmt_select FROM @sys.tmp.table_exists.SQL; IF (NOT v_error) THEN DEALLOCATE PREPARE stmt_select; SET out_exists = 'TEMPORARY'; END IF; END IF; END;
    '
    2017-04-04T15:59:29.758336Z 0 [ERROR] Aborting
    2017-04-04T15:59:33.078575Z 0 [Warning] TIMESTAMP with implicit DEFAULT value is deprecated. Please use --explicit_defaults_for_timestamp server option (see documentation for more details).
    2017-04-04T15:59:33.092082Z 0 [Note] /usr/sbin/mysqld (mysqld 5.7.17) starting as process 3326 ...
    2017-04-04T15:59:33.095074Z 0 [Note] InnoDB: PUNCH HOLE support available
    2017-04-04T15:59:33.095104Z 0 [Note] InnoDB: Mutexes and rw_locks use GCC atomic builtins
    2017-04-04T15:59:33.095109Z 0 [Note] InnoDB: Uses event mutexes
    2017-04-04T15:59:33.095112Z 0 [Note] InnoDB: GCC builtin __atomic_thread_fence() is used for memory barrier
    2017-04-04T15:59:33.095115Z 0 [Note] InnoDB: Compressed tables use zlib 1.2.3
    2017-04-04T15:59:33.095120Z 0 [Note] InnoDB: Using Linux native AIO
    2017-04-04T15:59:33.095340Z 0 [Note] InnoDB: Number of pools: 1
    2017-04-04T15:59:33.095428Z 0 [Note] InnoDB: Not using CPU crc32 instructions
    2017-04-04T15:59:33.096904Z 0 [Note] InnoDB: Initializing buffer pool, total size = 128M, instances = 1, chunk size = 128M
    2017-04-04T15:59:33.106888Z 0 [Note] InnoDB: Completed initialization of buffer pool
    2017-04-04T15:59:33.108711Z 0 [Note] InnoDB: If the mysqld execution user is authorized, page cleaner thread priority can be changed. See the man page of setpriority().
    2017-04-04T15:59:33.120189Z 0 [Note] InnoDB: Highest supported file format is Barracuda.
    2017-04-04T15:59:33.454908Z 0 [Note] InnoDB: Creating shared tablespace for temporary tables
    2017-04-04T15:59:33.455034Z 0 [Note] InnoDB: Setting file './ibtmp1' size to 12 MB. Physically writing the file full; Please wait ...
    2017-04-04T15:59:34.057704Z 0 [Note] InnoDB: File './ibtmp1' size is now 12 MB.
    2017-04-04T15:59:34.058603Z 0 [Note] InnoDB: 96 redo rollback segment(s) found. 96 redo rollback segment(s) are active.
    2017-04-04T15:59:34.058615Z 0 [Note] InnoDB: 32 non-redo rollback segment(s) are active.
    2017-04-04T15:59:34.063078Z 0 [Note] InnoDB: Waiting for purge to start
    2017-04-04T15:59:34.113304Z 0 [Note] InnoDB: 5.7.17 started; log sequence number 2536157
    2017-04-04T15:59:34.113841Z 0 [Note] InnoDB: Loading buffer pool(s) from /var/lib/mysql/ib_buffer_pool
    2017-04-04T15:59:34.114310Z 0 [Note] Plugin 'FEDERATED' is disabled.
    2017-04-04T15:59:34.118690Z 0 [Note] Found ca.pem, server-cert.pem and server-key.pem in data directory. Trying to enable SSL support using them.
    2017-04-04T15:59:34.118921Z 0 [Warning] CA certificate ca.pem is self signed.
    2017-04-04T15:59:34.119582Z 0 [Note] InnoDB: Buffer pool(s) load completed at 170404 23:59:34
    2017-04-04T15:59:34.237643Z 0 [Note] Server hostname (bind-address): '*'; port: 3306
    2017-04-04T15:59:34.241687Z 0 [Note] IPv6 is available.
    2017-04-04T15:59:34.241727Z 0 [Note]   - '::' resolves to '::';
    2017-04-04T15:59:34.241753Z 0 [Note] Server socket created on IP: '::'.
    2017-04-04T15:59:34.313591Z 0 [Note] Event Scheduler: Loaded 0 events
    2017-04-04T15:59:34.313686Z 0 [Note] Executing 'SELECT * FROM INFORMATION_SCHEMA.TABLES;' to get a list of tables using the deprecated partition engine. You may use the startup option '--disable-partition-engine-check' to skip this check.
    2017-04-04T15:59:34.313693Z 0 [Note] Beginning of list of non-natively partitioned tables
    2017-04-04T15:59:34.322126Z 0 [Note] End of list of non-natively partitioned tables
    2017-04-04T15:59:34.322261Z 0 [Note] /usr/sbin/mysqld: ready for connections.
    Version: '5.7.17'  socket: '/var/lib/mysql/mysql.sock'  port: 3306  MySQL Community Server (GPL)

關於MySQL數據庫的管理員帳號root,其密碼也再也不是空,而是安裝時隨機生成一個,這種處理方式必定程度上加強了MySQl服務器的安全性。隨機生成的密碼字串能夠從保存到mysql日誌文件中找到:

    [root@dbsvr1 pub]#grep 'temporary password' /var/log/mysqld.log
    2017-04-04T15:59:09.711439Z 1 [Note] A temporary password is generated for root@localhost: ;%7SDdD)quOI

3)確認安裝後的服務單元文件、服務狀態

查看服務單元文件

    [root@dbsvr1 pub]# ls -lh /usr/lib/systemd/system/mysqld.service
    -rw-r--r--. 1 root root 1.6K 11月 29 04:30 /usr/lib/systemd/system/mysqld.service

mysql服務的自啓狀態爲enabled:

    [root@dbsvr1 ~]# # systemctl  is-enabled  mysqld.service
    enabled

步驟三:查看Mysql服務的運行狀態

服務器進程爲mysqld,監聽的默認端口爲TCP 3306:

    [root@dbsvr1 pub]# netstat -antpu | grep mysql
    tcp6       0      0 :::3306                 :::*                    LISTEN      3913/mysqld        

查看Mysql服務的狀態

    [root@dbsvr1 pub]#systemctl  is-active  mysqld.service
    active
    [root@dbsvr1 pub]#systemctl  status mysqld.service
    mysqld.service - MySQL Server
       Loaded: loaded (/usr/lib/systemd/system/mysqld.service; enabled)
       Active: active (running) since 日 2017-04-23 08:56:24 CST; 1s ago
         Docs: man:mysqld(8)
               http://dev.mysql.com/doc/refman/en/using-systemd.html
      Process: 13753 ExecStart=/usr/sbin/mysqld --daemonize --pid-file=/var/run/mysqld/mysqld.pid $MYSQLD_OPTS (code=exited, status=0/SUCCESS)
      Process: 13732 ExecStartPre=/usr/bin/mysqld_pre_systemd (code=exited, status=0/SUCCESS)
     Main PID: 13757 (mysqld)
       CGroup: /system.slice/mysqld.service
               └─13757 /usr/sbin/mysqld --daemonize --pid-file=/var/run/mysqld/mysqld.pid

數據庫的默認存放位置爲 /var/lib/mysql:

    [root@dbsvr1 pub]# ls  /var/lib/mysql
    auto.cnf    client-cert.pem  ibdata1      ibtmp1      mysql.sock.lock     public_key.pem   sys
    ca-key.pem  client-key.pem   ib_logfile0  mysql       performance_schema  server-cert.pem
    ca.pem      ib_buffer_pool   ib_logfile1  mysql.sock  private_key.pem     server-key.pem

步驟四:鏈接MySQL服務器,修改密碼

查看隨機生成的root管理密碼

    [root@dbsvr1 pub]#grep 'temporary password' /var/log/mysqld.log
    2017-04-01T18:10:42.948679Z 1 [Note] A temporary password is generated for root@localhost: GWphBZ_g+1&          //密碼爲GWphBZ_g+1&

2)使用客戶端命令mysql鏈接到MySQL服務器

提示驗證時,填入前一步得到的隨機密碼,驗證成功後便可進入「mysql> 」環境:

    [root@dbsvr1 pub]# mysql -u root -p
    Welcome to the MySQL monitor.  Commands end with ; or \g.
    Your MySQL connection id is 14
    Server version: 5.7.17
    Copyright (c) 2000, 2016, 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>                                     //登陸成功後,進入SQL操做環境

用該密碼登陸到服務端後,必須立刻修改密碼,否則會報以下錯誤:

    mysql> show databases;
    ERROR 1820 (HY000): You must reset your password using ALTER USER statement before executing this statement.

3)執行SET PASSWORD命令修改密碼

這個其實與validate_password_policy的值有關,默認爲1,因此剛開始設置的密碼必須符合長度,且必須含有數 字,小寫或大寫字母,特殊字符。若是咱們不但願密碼設置的那麼複雜,須要修改兩個全局參數:validate_password_policy與 validate_password_length。validate_password_length默認值爲8,最小值爲4,若是你顯性指定 validate_password_length的值小於4,儘管不會報錯,但validate_password_length的值將設爲4。     //設置密碼長度是密碼最小長度值,設置的密碼不得小於最小值

可參考下列指令:

    mysql>set global validate_password_policy=0;
    mysql>set global validate_password_length=4;
    mysql> SET PASSWORD FOR 'root'@'localhost'=PASSWORD('1234567');
    Query OK, 0 rows affected, 1 warning (0.00 sec)

上述操做的結果是——更改數據庫用戶root從本機訪問時的密碼,設爲1234567。

退出「mysql> 」環境,從新登陸驗證,必須採用新的密碼才能登入:

    mysql> exit                                  //退出 mysql> 環境
    Bye
    [root@dbsvr1 ~]# mysql -u root –p            //從新登陸
    Enter password:                              //輸入新設置的密碼
    Welcome to the MySQL monitor.  Commands end with ; or \g.
    Your MySQL connection id is 15
    Server version: 5.7.17 MySQL Community Server (GPL)
    Copyright (c) 2000, 2016, 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> mysql> show databases;
    +--------------------+
    | Database           |
    +--------------------+
    | information_schema |
    | mysql              |
    | performance_schema |
    | sys                |
    +--------------------+
    4 rows in set (0.07 sec)

2、 數據庫基本管理

目標:

本案例要求熟悉MySQL的鏈接及數據庫表的增刪改查等基本管理操做,主要完成如下幾個方便的操做:

    使用mysql命令鏈接數據庫
    練習查看/刪除/建立庫的相關操做
    練習查看/刪除/建立表的相關操做,表數據參考如表-1所示內容
           

步驟:

步驟一:使用mysql命令鏈接數據庫

鏈接MySQL服務器時,最基本的用法是經過 -u 選項指定用戶名、-p指定密碼。密碼能夠寫在命令行(若是不寫,則出現交互,要求用戶輸入),固然基於安全考慮通常不推薦這麼作:

    [root@dbsvr1 ~]# mysql -uroot -p123456          //緊挨着選項,不要空格
    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 16
    Server version: 5.7.17 MySQL Community Server (GPL)
    Copyright (c) 2000, 2016, 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> exit                                  //退出已登陸的mysql> 環境
    Bye

默認狀況下,msyql命令會鏈接本機的MySQL服務。但在須要的時候,能夠經過 -h 選項指定遠程主機;若是端口不是3306,還能夠經過大寫的 -P 選項指定:

    [root@dbsvr1 ~]# mysql -u root -p -h 127.0.0.1 -P 3306
    Enter password:
    Welcome to the MySQL monitor.  Commands end with ; or \g.
    Your MySQL connection id is 17
    Server version: 5.7.17 MySQL Community Server (GPL)
    Copyright (c) 2000, 2016, 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> exit                                  //退出已登陸的mysql> 環境
    Bye

鏈接其餘主機的MySQL服務,有一個前提條件——對方已經添加了此用戶今後客戶機訪問的數據庫受權,受權操做方法會在後續課程學習。

步驟二:練習查看/刪除/建立庫的相關操做

以root用戶登入「mysql> 」環境後,能夠執行各類MySQL指令、SQL指令。基本的用法事項以下:

  •     操做指令不區分大小寫(庫名/表名、密碼、變量值等除外)。
  •     每條SQL指令以 ; 結束或分隔。
  •     不支持 Tab 鍵自動補齊。
  •     \c 可廢棄當前編寫錯的操做指令。

1)查看現有的庫

    mysql> SHOW DATABASES;
    +--------------------+
    | Database            |
    +--------------------+
    | information_schema |                              //信息概要庫
    | mysql               |                              //受權庫
    | performance_schema |                              //性能結構庫
    | sys                  |                              //系統元數據庫
    +--------------------+
    4 rows in set (0.15 sec)

2)切換/使用指定的庫

切換到sys庫:

    mysql> USE sys;
    Database changed
    mysql> SELECT DATABASE();                          //確認當前所在的庫
    +------------+
    | DATABASE() |
    +------------+
    | sys         |
    +------------+
    1 row in set (0.00 sec)

切換到mysql庫:

    mysql> USE mysql;
    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
    mysql> SELECT DATABASE();                          //確認當前所在的庫
    +------------+
    | DATABASE() |
    +------------+
    | mysql      |
    +------------+
    1 row in set (0.00 sec)

3)建立新的庫

新建名爲mydb的庫,確認結果:

    mysql> CREATE DATABASE mydb;
    Query OK, 1 row affected (0.00 sec)
    mysql> SHOW DATABASES;
    +--------------------+
    | Database           |
    +--------------------+
    | information_schema |
    | mydb               |                          //新建的mydb庫
    | mysql              |
    | performance_schema |
    | sys               |
    +--------------------+
    5 rows in set (0.00 sec)

新建名爲newdb的庫,確認結果:

    mysql> CREATE DATABASE newdb;
    Query OK, 1 row affected (0.00 sec)
    mysql> SHOW DATABASES;
    +--------------------+
    | Database            |
    +--------------------+
    | information_schema |
    | mydb                |                          //新建的mydb庫
    | mysql               |
    | newdb               |                          //新建的newdb庫
    | performance_schema |
    | sys                 |
    +--------------------+
    6 rows in set (0.00 sec)

新建數據庫之後,會爲每一個數據庫創建同名文件夾,可從命令行確認:

    [root@dbsvr1 ~]# ls -l /var/lib/mysql/{my,new}db/
    /var/lib/mysql/mydb/:
    總用量 4
    -rw-r-----. 1 mysql mysql 65 4月   2 03:14 db.opt
    /var/lib/mysql/newdb/:
    總用量 4
    -rw-r-----. 1 mysql mysql 65 4月   2 03:15 db.opt

4)刪除指定的庫

刪除名爲newdb的庫:

    mysql> DROP DATABASE newdb;
    Query OK, 0 rows affected (0.04 sec)
    mysql> SHOW DATABASES;                          //確認刪除結果,已無newdb表
    +--------------------+
    | Database           |
    +--------------------+
    | information_schema |
    | mydb               |
    | mysql              |
    | performance_schema |
    | sys                 |
    +--------------------+
    5 rows in set (0.00 sec)

步驟三:練習查看/刪除/建立表的相關操做

1)查看指定的庫裏有哪些表

查看mysql庫裏有哪些表:

    mysql> USE mysql;
    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
    mysql> SHOW TABLES;
    +---------------------------+
    | Tables_in_mysql           |
    +---------------------------+
    | columns_priv              |
    | db                        |
    | engine_cost               |
    | event                     |
    | func                      |
    | general_log               |
    | gtid_executed             |
    | help_category             |
    | help_keyword              |
    | help_relation             |
    | help_topic                |
    | innodb_index_stats        |
    | innodb_table_stats        |
    | ndb_binlog_index          |
    | plugin                    |
    | proc                      |
    | procs_priv                |
    | proxies_priv              |
    | server_cost               |
    | servers                   |
    | slave_master_info         |
    | slave_relay_log_info      |
    | slave_worker_info         |
    | slow_log                  |
    | tables_priv               |
    | time_zone                 |
    | time_zone_leap_second     |
    | time_zone_name            |
    | time_zone_transition      |
    | time_zone_transition_type |
    | user                      |                     //存放數據庫用戶的表
    +---------------------------+
    31 rows in set (0.00 sec)

2)查看指定表的字段結構

當前庫爲mysql,查看columns_priv表的結構,以列表形式展示:

    mysql> DESCRIBE columns_priv\G              //末尾不用分號
    *************************** 1. row ***************************
      Field: Host
       Type: char(60)
       Null: NO
        Key: PRI
    Default:
      Extra:
    *************************** 2. row ***************************
      Field: Db
       Type: char(64)
       Null: NO
        Key: PRI
    Default:
      Extra:
    *************************** 3. row ***************************
      Field: User
       Type: char(32)
       Null: NO
        Key: PRI
    Default:
      Extra:
    *************************** 4. row ***************************
      Field: Table_name
       Type: char(64)
       Null: NO
        Key: PRI
    Default:
      Extra:
    *************************** 5. row ***************************
      Field: Column_name
       Type: char(64)
       Null: NO
        Key: PRI
    Default:
      Extra:
    *************************** 6. row ***************************
      Field: Timestamp
       Type: timestamp
       Null: NO
        Key:
    Default: CURRENT_TIMESTAMP
      Extra: on update CURRENT_TIMESTAMP
    *************************** 7. row ***************************
      Field: Column_priv
       Type: set('Select','Insert','Update','References')
       Null: NO
        Key:
    Default:
      Extra:
    7 rows in set (0.01 sec)

查看columns_priv表的結構,以表格形式展示:

    mysql> DESCRIBE columns_priv;                  //末尾須要有分號
    +-------------+----------------------------------------------+------+-----+-------------------+-----------------------------+
    | Field       | Type                                         | Null | Key | Default           | Extra                       |
    +-------------+----------------------------------------------+------+-----+-------------------+-----------------------------+
    | Host        | char(60)                                     | NO   | PRI |                   |                             |
    | Db          | char(64)                                     | NO   | PRI |                   |                             |
    | User        | char(32)                                     | NO   | PRI |                   |                             |
    | Table_name  | char(64)                                     | NO   | PRI |                   |                             |
    | Column_name | char(64)                                     | NO   | PRI |                   |                             |
    | Timestamp   | timestamp                                    | NO   |     | CURRENT_TIMESTAMP | on update CURRENT_TIMESTAMP |
    | Column_priv | set('Select','Insert','Update','References') | NO   |     |                   |                             |
    +-------------+----------------------------------------------+------+-----+-------------------+-----------------------------+
    7 rows in set (0.00 sec)

上述操做中,DESCRIBE可縮寫爲DESC;另外,當引用非當前庫中的表時,能夠用「庫名.表名」的形式。好比,切換爲mysql庫再執行「DESCRIBE columns_priv;」,與如下操做的效果是相同的:

    mysql> DESC mysql.columns_priv;
    +-------------+----------------------------------------------+------+-----+-------------------+-----------------------------+
    | Field       | Type                                         | Null | Key | Default           | Extra                       |
    +-------------+----------------------------------------------+------+-----+-------------------+-----------------------------+
    | Host        | char(60)                                     | NO   | PRI |                   |                             |
    | Db          | char(64)                                     | NO   | PRI |                   |                             |
    | User        | char(16)                                     | NO   | PRI |                   |                             |
    | Table_name  | char(64)                                     | NO   | PRI |                   |                             |
    | Column_name | char(64)                                     | NO   | PRI |                   |                             |
    | Timestamp   | timestamp                                    | NO   |     | CURRENT_TIMESTAMP | on update CURRENT_TIMESTAMP |
    | Column_priv | set('Select','Insert','Update','References') | NO   |     |                   |                             |
    +-------------+----------------------------------------------+------+-----+-------------------+-----------------------------+
    7 rows in set (0.00 sec)

3)在test庫中建立一個名爲pwlist的表

包括name、password兩列,其中name列做爲主鍵。兩個字段值均不容許爲空,其中密碼列賦予默認空值,相關操做以下所述。

切換到mydb庫:

    mysql> USE mydb;
    Database changed

新建pwlist表:

    mysql> CREATE TABLE pwlist(
        -> name CHAR(16) NOT NULL,
        -> password CHAR(48) DEFAULT '',
        -> PRIMARY KEY(name)
        -> );
    Query OK, 0 rows affected (0.38 sec)

確認新建立的表:

    mysql> SHOW TABLES;
    +----------------+
    | Tables_in_mydb |
    +----------------+
    | pwlist         |                                  //新建的pwlist表
    +----------------+
    1 rows in set (0.01 sec)

查看pwlist表的字段結構:

    mysql> DESC pwlist;
    +----------+----------+------+-----+---------+-------+
    | Field    | Type     | Null | Key | Default | Extra |
    +----------+----------+------+-----+---------+-------+
    | name     | char(16) | NO   | PRI | NULL    |       |
    | password | char(48) | YES  |     |         |       |
    +----------+----------+------+-----+---------+-------+
    2 rows in set (0.01 sec)

4)刪除指定的表

刪除當前庫中的pwlist表:

    mysql> DROP TABLE pwlist;
    Query OK, 0 rows affected (0.01 sec)

確認刪除結果:

    mysql> SHOW TABLES;
    Empty set (0.00 sec)

5)在mydb庫中建立一個學員表

表格結構及數據內容如表-1所示。

在MySQL表內存儲中文數據時,須要更改字符集(默認爲latin1不支持中文),以便MySQL支持存儲中文數據記錄;好比,能夠在建立庫或表的時候,手動添加「DEFAULT CHARSET=utf8」來更改字符集。

根據上述表格結構,建立支持中文的student表:

    mysql> CREATE TABLE mydb.student(
        -> 學號 char(9) NOT NULL,
        -> 姓名 varchar(4) NOT NULL,
        -> 性別 enum('男','女') NOT NULL,
        -> 手機號 char(11) DEFAULT '',
        -> 通訊地址 varchar(64),
        -> PRIMARY KEY(學號)
        -> ) DEFAULT CHARSET=utf8;                  //手工指定字符集,採用utf8
    Query OK, 0 rows affected (0.31sec)

查看student表的字段結構:

    mysql> DESC mydb.student;
    +--------------+-------------------+------+-----+---------+-------+
    | Field        | Type              | Null | Key | Default | Extra |
    +--------------+-------------------+------+-----+---------+-------+
    | 學號         | char(9)           | NO   | PRI | NULL    |       |
    | 姓名         | varchar(4)        | NO   |     | NULL    |       |
    | 性別         | enum('男','女')   | NO   |     | NULL    |       |
    | 手機號       | char(11)          | YES  |     |         |       |
    | 通訊地址     | varchar(64)       | YES  |     | NULL    |       |
    +--------------+-------------------+------+-----+---------+-------+
    5 rows in set (0.04 sec)

查看student表的實際建立指令:

    mysql> SHOW CREATE TABLE mydb.student;
    +---------+--------------------------------------------------------------------------------------------------------------------------------+
    | Table   | Create Table                                                                                                                                            |
    +---------+---------------------------------------------------------------------------------------------------------------------------------+
    | student | CREATE TABLE `student` (
      `學號` char(9) NOT NULL,
      `姓名` varchar(4) NOT NULL,
      `性別` enum('男','女') NOT NULL,
      `手機號` char(11) DEFAULT '',
      `通訊地址` varchar(64) DEFAULT NULL,
      PRIMARY KEY (`學號`)
    ) ENGINE=InnoDB DEFAULT CHARSET=utf8                  |
    +---------+---------------------------------------------------------------------------------------------------------------------------------+
    1 row in set (0.00 sec)

注意:若要修改MySQL服務的默認字符集,能夠更改服務器的my.cnf配置文件,添加character_set_server=utf8 配置,而後重啓數據庫服務。

    [root@dbsvr1 ~]# vim /etc/my.cnf                          //修改運行服務配置
    [mysqld]
    .. ..
    character_set_server=utf8
    [root@dbsvr1 ~]# systemctl restart mysqld                  //重啓服務
    .. ..
    [root@dbsvr1 ~]# mysql –u root -p  
    Enter password:
    .. ..
    mysql> SHOW VARIABLES LIKE 'character%';                  //確認更改結果
    +--------------------------+----------------------------+
    | Variable_name            | Value                      |
    +--------------------------+----------------------------+
    | character_set_client     | utf8                       |
    | character_set_connection | utf8                       |
    | character_set_database   | utf8                       |
    | character_set_filesystem | binary                     |
    | character_set_results    | utf8                       |
    | character_set_server     | utf8                       |
    | character_set_system     | utf8                       |
    | character_sets_dir       | /usr/share/mysql/charsets/ |
    +--------------------------+----------------------------+
    8 rows in set (0.03 sec)

3、MySQL 數據類型

目標:

本案例要求熟悉MySQL的字段數據類型、時間函數的使用,完成如下任務操做:

  •     在home庫裏建立famliy表,表結構、字段類型自定義
  •     練習各類時間函數的使用

步驟:

步驟一:建立home庫、family表

1)新建home庫,並切換到home庫

    mysql> CREATE DATABASE home;
    Query OK, 1 row affected (0.00 sec)
    mysql> USE home;
    Database changed

2)新建family表

假定family表用來記錄每一個家庭成員的姓名(name)、性別(gender)、出生日期(birth)、職業(job)、與戶主關係(relation)。

    mysql> CREATE TABLE family(
        -> name varchar(16) NOT NULL,
        -> gender enum('male','femal') DEFAULT 'male',
        -> birth date NOT NULL,
        -> job varchar(16) DEFAULT '',
        -> relation varchar(24) NOT NULL,
        -> PRIMARY KEY(name)
        -> );
    Query OK, 0 rows affected (0.61sec)

查看family表的字段結構:

    mysql> DESC family;
    +----------+----------------------+------+-----+---------+-------+
    | Field    | Type                 | Null | Key | Default | Extra |
    +----------+----------------------+------+-----+---------+-------+
    | name     | varchar(16)          | NO   | PRI | NULL    |       |
    | gender   | enum('male','femal') | YES  |     | male    |       |
    | birth    | date                 | NO   |     | NULL    |       |
    | job      | varchar(16)          | YES  |     |         |       |
    | relation | varchar(24)          | NO   |     | NULL    |       |
    +----------+----------------------+------+-----+---------+-------+
    5 rows in set (0.00 sec)

步驟二:練習各類時間函數的使用

1)使用now()查看當前的日期和時間

    mysql> SELECT now();
    +---------------------+
    | now()               |
    +---------------------+
    | 2017-04-02 04:02:42 |
    +---------------------+
    1 row in set (0.00 sec)

2)使用sysdate()查看系統日期和時間

    mysql> SELECT sysdate();
    +---------------------+
    | sysdate()           |
    +---------------------+
    | 2017-04-02 04:03:21 |
    +---------------------+
    1 row in set (0.00 sec)

3)使用curdate()得到當前的日期,不含時間

    mysql> SELECT curdate();
    +------------+
    | curdate()  |
    +------------+
    | 2017-04-02 |
    +------------+
    1 row in set (0.00 sec)

4)使用curtime()得到當前的時間,不含日期

    mysql> SELECT curtime();
    +-----------+
    | curtime() |
    +-----------+
    | 04:04:55  |
    +-----------+
    1 row in set (0.00 sec)

5)分別獲取當前日期時間中的年份、月份、日

    mysql> SELECT year(now()),month(now()),day(now());
    +-------------+--------------+------------+
    | year(now()) | month(now()) | day(now()) |
    +-------------+--------------+------------+
    |        2017 |            4 |          2 |
    +-------------+--------------+------------+
    1 row in set (0.00 sec)

6)獲取系統日期時間中的月份、日

    mysql> SELECT month(sysdate()),day(sysdate());
    +------------------+----------------+
    | month(sysdate()) | day(sysdate()) |
    +------------------+----------------+
    |                4 |              2 |
    +------------------+----------------+
    1 row in set (0.00 sec)

7)獲取系統日期時間中的時刻

    mysql> SELECT time(sysdate());
    +-----------------+
    | time(sysdate()) |
    +-----------------+
    | 04:06:08        |
    +-----------------+
    1 row in set (0.00 sec)

4、表結構的調整

目標:

本案例要求熟悉MySQL庫中表的字段修改,主要練習如下操做:

  •     添加字段
  •     修改字段名
  •     修改字段類型
  •     刪除字段

步驟:

步驟一:添加字段

在home中建立tea6表

    mysql> CREATE TABLE home.tea6(id int(4) PRIMARY KEY,
        -> name varchar(4) NOT NULL,
        -> age int(2) NOT NULL
        -> );
    Query OK, 0 rows affected (0.34 sec)

爲tea6表添加一個address字段

添加前:

    mysql> DESC tea6;
    +-------+------------+------+-----+---------+-------+
    | Field | Type       | Null | Key | Default | Extra |
    +-------+------------+------+-----+---------+-------+
    | id    | int(4)     | NO   | PRI | NULL    |       |
    | name  | varchar(4) | NO   |     | NULL    |       |
    | age   | int(2)     | NO   |     | NULL    |       |
    +-------+------------+------+-----+---------+-------+
    3 rows in set (0.00 sec)

添加address字段:

    mysql> ALTER TABLE tea6 ADD address varchar(48);
    Query OK, 0 rows affected (0.84 sec)
    Records: 0  Duplicates: 0  Warnings: 0

添加後(默認做爲最後一個字段):

    mysql> DESC tea6;
    +---------+-------------+------+-----+---------+-------+
    | Field   | Type        | Null | Key | Default | Extra |
    +---------+-------------+------+-----+---------+-------+
    | id      | int(4)      | NO   | PRI | NULL    |       |
    | name    | varchar(4)  | NO   |     | NULL    |       |
    | age     | int(2)      | NO   |     | NULL    |       |
    | address | varchar(48) | YES  |     | NULL    |       |
    +---------+-------------+------+-----+---------+-------+
    4 rows in set (0.00 sec)

3)在tea6表的age列以後添加一個gender字段

添加操做:

    mysql> ALTER TABLE tea6 ADD gender enum('boy','girl') AFTER age;
    Query OK, 0 rows affected (0.59 sec)
    Records: 0  Duplicates: 0  Warnings: 0

確認添加結果:

    mysql> DESC tea6;
    +---------+--------------------+------+-----+---------+-------+
    | Field   | Type               | Null | Key | Default | Extra |
    +---------+--------------------+------+-----+---------+-------+
    | id      | int(4)             | NO   | PRI | NULL    |       |
    | name    | varchar(4)         | NO   |     | NULL    |       |
    | age     | int(2)             | NO   |     | NULL    |       |
    | gender  | enum('boy','girl') | YES  |     | NULL    |       |
    | address | varchar(48)        | YES  |     | NULL    |       |
    +---------+--------------------+------+-----+---------+-------+
    5 rows in set (0.00 sec)

步驟二:修改字段名和字段類型

將tea6表的gender字段更名爲sex,並添加非空約束

修改操做:

    mysql> ALTER TABLE tea6 CHANGE gender
        -> sex enum('boy','girl') NOT NULL;
    Query OK, 0 rows affected (0.08 sec)
    Records: 0  Duplicates: 0  Warnings: 0

確認修改結果:

    mysql> DESC tea6;
    +---------+--------------------+------+-----+---------+-------+
    | Field   | Type               | Null | Key | Default | Extra |
    +---------+--------------------+------+-----+---------+-------+
    | id      | int(4)             | NO   | PRI | NULL    |       |
    | name    | varchar(4)         | NO   |     | NULL    |       |
    | age     | int(2)             | NO   |     | NULL    |       |
    | sex     | enum('boy','girl') | NO   |     | NULL    |       |
    | address | varchar(48)        | YES  |     | NULL    |       |
    +---------+--------------------+------+-----+---------+-------+
    5 rows in set (0.00 sec)

步驟三:刪除字段

刪除tea6表中名爲sex的字段:

    mysql> ALTER TABLE tea6 DROP sex;                             //刪除操做
    Query OK, 0 rows affected (0.52 sec)
    Records: 0  Duplicates: 0  Warnings: 0
    mysql> DESC tea6;                                          //確認刪除結果
    +---------+-------------+------+-----+---------+-------+
    | Field   | Type        | Null | Key | Default | Extra |
    +---------+-------------+------+-----+---------+-------+
    | id      | int(4)      | NO   | PRI | NULL    |       |
    | name    | varchar(4)  | NO   |     | NULL    |       |
    | age     | int(2)      | NO   |     | NULL    |       |
    | address | varchar(48) | YES  |     | NULL    |       |
    +---------+-------------+------+-----+---------+-------+
    4 rows in set (0.00 sec)

 

附加:

MySQL密碼強度審計插件:validate_password的使用說明
相信不少人在平常工做中,都會遇到設置用戶、密碼之類的問題,不少人使用keepass來生成和保存密碼;可是,不少人爲了易於記憶,會選擇相對簡答的密碼,這樣,在安全性方面,會存在很是嚴重的安全隱患。
在mysql 5.6對密碼的強度進行了增強,推出了validate_password 插件。支持密碼的強度要求。
此插件要求版本:5.6.6 以上版本
安裝方式:
1.安裝插件:(默認安裝了插件後,強度插件就啓用了,關閉,須要在配置文件假如相關關閉參數)
mysql>INSTALL PLUGIN validate_password SONAME 'validate_password.so';
2.配置文件添加部分參數:
[mysqld]
plugin-load=validate_password.so
validate_password_policy=2
validate-password=FORCE_PLUS_PERMANENT
3.以上處理後,就能夠測試了:
mysql> SET PASSWORD = PASSWORD('abc');
ERROR 1819 (HY000): Your password does not satisfy the current policy requirements
mysql> SET PASSWORD = '*0D3CED9BEC10A777AEC23CCC353A8C08A633045E';
Query OK, 0 rows affected (0.01 sec)
4.相關說明:
(1).相關選項:
validate-password=ON/OFF/FORCE/FORCE_PLUS_PERMANENT: 決定是否使用該插件(及強制/永久強制使用)。
validate_password_dictionary_file:插件用於驗證密碼強度的字典文件路徑。
validate_password_length:密碼最小長度。
validate_password_mixed_case_count:密碼至少要包含的小寫字母個數和大寫字母個數。
validate_password_number_count:密碼至少要包含的數字個數。
validate_password_policy:密碼強度檢查等級,0/LOW、1/MEDIUM、2/STRONG。
validate_password_special_char_count:密碼至少要包含的特殊字符數。
其中,關於validate_password_policy-密碼強度檢查等級:
0/LOW:只檢查長度。
1/MEDIUM:檢查長度、數字、大小寫、特殊字符。
2/STRONG:檢查長度、數字、大小寫、特殊字符字典文件。
(2).插件的安裝啓用:
插件對應的庫對象文件需在配置選項plugin_dir指定的目錄中。
可以使用--plugin-load=validate_password.so,在server啓動時載入插件,或者將plugin-load=validate_password.so寫入配置文件。
也能夠經過以下語句在server運行時載入插件(會註冊進mysql.plugins表)
mysql> INSTALL PLUGIN validate_password SONAME 'validate_password.so';
(3).爲阻止該插件在運行時被刪除可在配置文件中添加:
[mysqld]
plugin-load=validate_password.so
validate-password=FORCE_PLUS_PERMANENT

 

約束條件:not null 表示不容許空值

null(空值)、"null"(非空)、""(非空)、" "(非空)、NULL(非空)

 枚舉類型:set("read","run","movie","sing") default "read,run": 這種枚舉類型值能夠多選;   enum("boy","girl") default "boy":這種枚舉類型值只能單選。

數據庫初學總結

1、安裝mysql包並起服務:
前提準備:
# yum -y remove mariadb-server mariadb   //卸載系統自帶的數據庫
# rpm -qf /etc/my.cnf   //清理配置文件

   1> 安裝依賴包:perl-Data-Dumper、perl-JSON
# yum -y install perl-Data-Dumper perl-JSON

   2> 將須要安裝的包解壓到指定位置
# mkdir /opt/Database1
# tar -xf mysql-5.7.17-1.el7.x86_64.rpm-bundle.tar -C /opt/Database1/  //將包解壓縮到指定位置
   3> 命令cd進入指定包位置,刪掉不用的包
# cd /opt/Database1/
# rm -rf mysql-community-server-minimal-5.7.17-1.el7.x86_64.rpm  //刪掉最小化安裝包
   4> 將要用到的全部的rpm包安裝
# rpm -Uvh mysql-community-*.rpm   //升級方式安裝目錄下的一系列rpm包
   5> 啓動mysqld服務設置爲開機自啓動
# systemctl start mysqld
# systemctl enable mysqld
# netstat -antup|grep 3306   //查看端口狀態,是否啓動

2、基本的mysql操做
1> 更改數據庫登錄密碼
# grep 'password' /var/log/mysqld.log  //能夠查看數據庫默認的密碼 7ekt7,Yif;Ws
2018-01-17T04:30:06.339970Z 1 [Note] A temporary password is generated for root@localhost: 7ekt7,Yif;Ws
# mysql -u root -p'7ekt7,Yif;Ws'
mysql> set global validate_password_policy=0;
mysql> set global validate_password_length=6;
mysql> alter user root@"localhost" identified by "123456";
mysql> quit
# vim /etc/my.cnf   //修改mysql主配置文件
  4 [mysqld]
  5 validate_password_policy=0    //密碼強度檢查等級,0表示最低
  6 validate_password_length=6    //密碼最小長度是6位,默認是8位,最低可設置爲4位
# systemctl stop mysqld.service
# systemctl start mysqld.service
或者:
# systemctl restart mysqld.service
2> 基本的操做:
# mysql -u root -p'123456'   //-p後面緊跟密碼,最好加引號,引號能夠屏蔽特殊符號
mysql> show databases;   //查看數據庫,命令行後面必須加分號結束
mysql> use mysql;    //選擇想要的庫
mysql> select database();  //查看當前數據庫
mysql> show tables;      //查看當前數據庫裏的數據表
mysql> create database db1;   //建立數據庫,建立數據表前要先建立庫
mysql> create table db1.t2(   //建立數據表,注意數據表裏面至少有一條目錄才行
    -> name char(16),
    -> home float(8,2),
    -> phone tinyint(1),
    -> id smallint(1),
    -> country float(6,2)
        -> );
mysql> drop table db1.t2;   //刪掉數據表

mysql> create table stuinfo(      //建立數據表頭,設置了默認值的話,後面插入內容,沒有該值會自動補充會
    -> name char(16) not null,
    -> age tinyint(1) unsigned not null default 20,
    -> sex enum("boy","girl","other") not null default boy,
    -> birthday date not null default 19900101,
    -> love set("read","game","animal") not null default "read",
    -> mail varchar(30) not null default "18318888868@163.com",
    -> phone char(50) not null default "xiaomi",
    -> phoneprice tinyint(1) not null default 100
        -> );

mysql> insert into stuinfo values("tom","18","boy","19950808","game","15286822708@163.com","huawei","80");
//能夠直接插入值,默認是按照表頭對應順序日後填充,必須每項都填滿,不然報錯不匹配
mysql> insert into stuinfo(name,sex) values("jim","boy");   
//也能夠插入指定值到指定字段,有些沒有設定默認值的,插入時必須指定默認值

mysql> desc stuinfo;  //查看數據表stuinfo的字段
mysql> alter table stuinfo add home char(50) not null default "tianjing";   //數據表添加字段
mysql> alter table stuinfo drop home;    //數據表刪除字段
mysql> alter table stuinfo rename to stu;  //數據表更名字
mysql> alter table stuinfo modify love set("read","game","hiking") not null default "read,game,hiking";
//修改表字段信息,枚舉類型:set("a","b","c") 能夠多選;enum("a","b","c")只能單選。
mysql> alter table stuinfo modify sex set("boy","girl") not null default "boy";
//修改表字段信息,枚舉類型:set("a","b","c") 能夠多選;enum("a","b","c")只能單選。
mysql> alter table stuinfo modify love set('read','game','hiking') after name;
//挪動字段位置,須要挪動的字段類型信息也要跟上;
mysql> alter table student change love favourite set('read','game','hiking');
//給數據字段更名字

mysql> update stuinfo set age=22 where name="lucy";  //注意這個stuinfo表前面不用加table,加了反而語法錯誤;
mysql> delete from stuinfo where name="lucy";    //刪除數據表中的某個記錄
mysql> drop table t1;   //刪掉整個數據表,這裏是用相對路徑,能夠絕對路徑

Mysql 數據庫可參看這個網站:http://www.runoob.com/mysql/mysql-tutorial.html

 Mysql基本操做格式:

1> 建立數據庫&刪除數據庫

create  database  庫名;  //建立數據庫

drop  database  庫名;  //刪除數據庫

2> 建立數據表

create  table  庫名.表名(
字段名   類型(寬度)   約束條件,
字段名   類型(寬度)   約束條件,
.....
);

3> 查看錶結構

desc  庫名.表名;

4> 查看錶記錄信息

select  *  from  庫名.表名;

5> 插入表記錄信息

insert  into  庫.表  values("字符1","字符2",...,"字符n");      //這種方式向表裏插入的值要和表中全部字段一一匹配,不然報錯

insert  into  庫.表(字段名1,字段名2,...,字段名n)   values("字符1","字符2",...,"字符n");     //這種方式能夠向表裏指定的n個字段插入值,其餘字段值爲表格默認值

6> 更改表記錄信息

update  庫.表 set  字段名=「值「  where  約束條件;

7> 刪除表記錄信息

delete  from  庫.表;      //這種方式是刪除表記錄全部記錄

delete  from  庫.表  where 約束條件;  //這種方式刪除表記錄中特定條件的記錄

8> 修改表結構

格式:alter   table   庫.表    執行動做;

添加新字段 :
add    字段名      類型(寬度);
add    字段名      類型(寬度)   約束條件;
add    字段名      類型(寬度)   約束條件  first;
add    字段名      類型(寬度)   約束條件  after   字段名;
add    字段名      類型(寬度),add    字段名      類型(寬度);

刪除已有字段 : 
drop   字段名;
drop   字段名,drop   字段名;

修改字段類型: (修改的類型與字段已存儲的數據衝突,則不容許修改)
modify  字段名    類型(寬度)  約束條件;

修改字段名 :
change   源字段名  新字段名  類型(寬度)  約束條件;

修改表名:alter  table  源表名  rename   新表名;

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