MySQL語句使用。

来源:https://www.cnblogs.com/www233ii/archive/2019/11/23/11918158.html
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MySQL的DDL、DML、DQL語句和單表增、刪、改、查 [toc] 實驗準備： 1. 初始化設置過的centos虛擬機 2. 安裝MySQL資料庫 實驗開始： DDL語句 1. 創建和刪除資料庫 2. 查詢資料庫字元集 MariaDB [(none)] show create database ...


目錄

MySQL的DDL、DML、DQL語句和單表增、刪、改、查

實驗準備：

  1. 初始化設置過的centos虛擬機
  2. 安裝MySQL資料庫

實驗開始：

DDL語句

表：二維關係 設計表：遵循規範
定義：欄位，索引
欄位：欄位名，欄位數據類型，修飾符
約束，索引：應該創建在經常用作查詢條件的欄位上
  1. 創建和刪除資料庫
MariaDB [(none)]> create database testdb1;     (分號為結束符)
Query OK, 1 row affected (0.00 sec)

MariaDB [(none)]> show databases;  （列出所有資料庫）
+--------------------+
| Database           |
+--------------------+
| information_schema |
| mysql              |
| performance_schema |
| testdb1            |
+--------------------+
4 rows in set (0.00 sec)

[root@centos7 ~]#tree /data/mysql/testdb1/   （其實就是在MySQL下麵建立了一個目錄）
/data/mysql/testdb1/
└── db.opt

[root@centos7 ~]#cat /data/mysql/testdb1/db.opt （也可以查看裡面的內容，字元集也可以看到）
default-character-set=latin1
default-collation=latin1_swedish_ci
0 directories, 1 file

MariaDB [testdb1]> drop database testdb1;   （刪除資料庫，同時MySQL下麵的testdb1目錄也會刪除）
Query OK, 1 row affected (0.00 sec)

MariaDB [(none)]> show databases;
+--------------------+
| Database           |
+--------------------+
| hellodb            |
| information_schema |
| mysql              |
| performance_schema |
+--------------------+
4 rows in set (0.00 sec)
  1. 查詢資料庫字元集
MariaDB [(none)]> show create database testdb1;   (查看testdb1的資料庫字元集)
+----------+--------------------------------------------------------------------+
| Database | Create Database                                                    |
+----------+--------------------------------------------------------------------+
| testdb1  | CREATE DATABASE `testdb1` /*!40100 DEFAULT CHARACTER SET latin1 */ | （這裡最後的為字元集既latin1這個字元集不支持漢字的。）
+----------+--------------------------------------------------------------------+
1 row in set (0.00 sec)

(這樣也可以查看比較好辨認)
MariaDB [(none)]> show create database testdb1\G;
*************************** 1. row ***************************
       Database: testdb1
Create Database: CREATE DATABASE `testdb1` /*!40100 DEFAULT CHARACTER SET latin1 */
1 row in set (0.00 sec)

MariaDB [(none)]> show create database mysql; （查看MySQL的資料庫字元集）
+----------+------------------------------------------------------------------+
| Database | Create Database                                                  |
+----------+------------------------------------------------------------------+
| mysql    | CREATE DATABASE `mysql` /*!40100 DEFAULT CHARACTER SET latin1 */ |
+----------+------------------------------------------------------------------+
1 row in set (0.00 sec)
  1. 修改字元集
MariaDB [(none)]> alter database testdb1 CHARACTER SET utf8mb4; (這個字元集支持全球文字還支持表情包)
Query OK, 1 row affected (0.00 sec)

MariaDB [(none)]> show create database testdb1;
+----------+---------------------------------------------------------------------+
| Database | Create Database                                                     |
+----------+---------------------------------------------------------------------+
| testdb1  | CREATE DATABASE `testdb1` /*!40100 DEFAULT CHARACTER SET utf8mb4 */ |
+----------+---------------------------------------------------------------------+
1 row in set (0.00 sec)

[root@centos7 ~]#cat /data/mysql/testdb1/db.opt   (文件也會修改)
default-character-set=utf8mb4
default-collation=utf8mb4_general_ci
  1. 創建一個表做實驗
MariaDB [(none)]> use testdb1;
Database changed
MariaDB [testdb1]> create table test ( id int unsigned auto_increment primary key,name varchar(10) not null,mobile char(11) not null );
Query OK, 0 rows affected (0.01 sec)

MariaDB [testdb1]> desc test;   （查看表結構）
+--------+------------------+------+-----+---------+----------------+
| Field  | Type             | Null | Key | Default | Extra          |
+--------+------------------+------+-----+---------+----------------+
| id     | int(10) unsigned | NO   | PRI | NULL    | auto_increment |
| name   | varchar(10)      | NO   |     | NULL    |                |
| mobile | char(11)         | NO   |     | NULL    |                |
+--------+------------------+------+-----+---------+----------------+   
3 rows in set (0.00 sec)



MariaDB [hellodb]> show tables;   （列出當前庫里的所有表）
+-------------------+
| Tables_in_hellodb |
+-------------------+
| classes           |
| coc               |
| courses           |
| scores            |
| students          |
| teachers          |
| toc               |
+-------------------+
7 rows in set (0.01 sec)

(查看表內容，先要進入存在這個表的資料庫)  這個表是我從外部導入進來的沒有手工創建，需要的話下次我貼出來。
MariaDB [(none)]> use hellodb
Database changed
MariaDB [hellodb]> select * from students;
+-------+---------------+-----+--------+---------+-----------+
| StuID | Name          | Age | Gender | ClassID | TeacherID |
+-------+---------------+-----+--------+---------+-----------+
|     1 | Shi Zhongyu   |  22 | M      |       2 |         3 |
|     2 | Shi Potian    |  22 | M      |       1 |         7 |
|     3 | Xie Yanke     |  53 | M      |       2 |        16 |
|     4 | Ding Dian     |  32 | M      |       4 |         4 |
|     5 | Yu Yutong     |  26 | M      |       3 |         1 |
|     6 | Shi Qing      |  46 | M      |       5 |      NULL |
|     7 | Xi Ren        |  19 | F      |       3 |      NULL |
|     8 | Lin Daiyu     |  17 | F      |       7 |      NULL |
|     9 | Ren Yingying  |  20 | F      |       6 |      NULL |
|    10 | Yue Lingshan  |  19 | F      |       3 |      NULL |
|    11 | Yuan Chengzhi |  23 | M      |       6 |      NULL |
|    12 | Wen Qingqing  |  19 | F      |       1 |      NULL |
|    13 | Tian Boguang  |  33 | M      |       2 |      NULL |
|    14 | Lu Wushuang   |  17 | F      |       3 |      NULL |
|    15 | Duan Yu       |  19 | M      |       4 |      NULL |
|    16 | Xu Zhu        |  21 | M      |       1 |      NULL |
|    17 | Lin Chong     |  25 | M      |       4 |      NULL |
|    18 | Hua Rong      |  23 | M      |       7 |      NULL |
|    19 | Xue Baochai   |  18 | F      |       6 |      NULL |
|    20 | Diao Chan     |  19 | F      |       7 |      NULL |
|    21 | Huang Yueying |  22 | F      |       6 |      NULL |
|    22 | Xiao Qiao     |  20 | F      |       1 |      NULL |
|    23 | Ma Chao       |  23 | M      |       4 |      NULL |
|    24 | Xu Xian       |  27 | M      |    NULL |      NULL |
|    25 | Sun Dasheng   | 100 | M      |    NULL |      NULL |
+-------+---------------+-----+--------+---------+-----------+
25 rows in set (0.00 sec)

（創建表獲取幫助命令）
MariaDB [hellodb]> help create table;
Name: 'CREATE TABLE'
Description:
Syntax:
CREATE [TEMPORARY] TABLE [IF NOT EXISTS] tbl_name
    (create_definition,...)
    [table_options]
    [partition_options]

Or:

CREATE [TEMPORARY] TABLE [IF NOT EXISTS] tbl_name
    [(create_definition,...)]
    [table_options]
    [partition_options]
    select_statement

Or:

CREATE [TEMPORARY] TABLE [IF NOT EXISTS] tbl_name
    { LIKE old_tbl_name | (LIKE old_tbl_name) }
  1. 克隆表
MariaDB [hellodb]> create table newstudents select * from students;  （通過查詢現存表創建；新表會被直接插入查詢而來的數據）
Query OK, 25 rows affected (0.01 sec)
Records: 25  Duplicates: 0  Warnings: 0

MariaDB [hellodb]> show tables;
+-------------------+
| Tables_in_hellodb |
+-------------------+
| classes           |
| coc               |
| courses           |
| newstudents       |
| scores            |
| students          |
| teachers          |
| toc               |
+-------------------+
8 rows in set (0.00 sec)

MariaDB [hellodb]> select * from newstudents;
+-------+---------------+-----+--------+---------+-----------+
| StuID | Name          | Age | Gender | ClassID | TeacherID |
+-------+---------------+-----+--------+---------+-----------+
|     1 | Shi Zhongyu   |  22 | M      |       2 |         3 |
|     2 | Shi Potian    |  22 | M      |       1 |         7 |
|     3 | Xie Yanke     |  53 | M      |       2 |        16 |
|     4 | Ding Dian     |  32 | M      |       4 |         4 |
|     5 | Yu Yutong     |  26 | M      |       3 |         1 |
|     6 | Shi Qing      |  46 | M      |       5 |      NULL |
|     7 | Xi Ren        |  19 | F      |       3 |      NULL |
|     8 | Lin Daiyu     |  17 | F      |       7 |      NULL |
|     9 | Ren Yingying  |  20 | F      |       6 |      NULL |
|    10 | Yue Lingshan  |  19 | F      |       3 |      NULL |
|    11 | Yuan Chengzhi |  23 | M      |       6 |      NULL |
|    12 | Wen Qingqing  |  19 | F      |       1 |      NULL |
|    13 | Tian Boguang  |  33 | M      |       2 |      NULL |
|    14 | Lu Wushuang   |  17 | F      |       3 |      NULL |
|    15 | Duan Yu       |  19 | M      |       4 |      NULL |
|    16 | Xu Zhu        |  21 | M      |       1 |      NULL |
|    17 | Lin Chong     |  25 | M      |       4 |      NULL |
|    18 | Hua Rong      |  23 | M      |       7 |      NULL |
|    19 | Xue Baochai   |  18 | F      |       6 |      NULL |
|    20 | Diao Chan     |  19 | F      |       7 |      NULL |
|    21 | Huang Yueying |  22 | F      |       6 |      NULL |
|    22 | Xiao Qiao     |  20 | F      |       1 |      NULL |
|    23 | Ma Chao       |  23 | M      |       4 |      NULL |
|    24 | Xu Xian       |  27 | M      |    NULL |      NULL |
|    25 | Sun Dasheng   | 100 | M      |    NULL |      NULL |
+-------+---------------+-----+--------+---------+-----------+
25 rows in set (0.00 sec)

（註意：這樣不會把主鍵之類的複製過來，只是複製數據，表結構不一樣）如下：
MariaDB [hellodb]> desc newstudents;
+-----------+---------------------+------+-----+---------+-------+
| Field     | Type                | Null | Key | Default | Extra |
+-----------+---------------------+------+-----+---------+-------+
| StuID     | int(10) unsigned    | NO   |     | 0       |       |
| Name      | varchar(50)         | NO   |     | NULL    |       |
| Age       | tinyint(3) unsigned | NO   |     | NULL    |       |
| Gender    | enum('F','M')       | NO   |     | NULL    |       |
| ClassID   | tinyint(3) unsigned | YES  |     | NULL    |       |
| TeacherID | int(10) unsigned    | YES  |     | NULL    |       |
+-----------+---------------------+------+-----+---------+-------+
6 rows in set (0.00 sec)

MariaDB [hellodb]> desc students;
+-----------+---------------------+------+-----+---------+----------------+
| Field     | Type                | Null | Key | Default | Extra          |
+-----------+---------------------+------+-----+---------+----------------+
| StuID     | int(10) unsigned    | NO   | PRI | NULL    | auto_increment |
| Name      | varchar(50)         | NO   |     | NULL    |                |
| Age       | tinyint(3) unsigned | NO   |     | NULL    |                |
| Gender    | enum('F','M')       | NO   |     | NULL    |                |
| ClassID   | tinyint(3) unsigned | YES  |     | NULL    |                |
| TeacherID | int(10) unsigned    | YES  |     | NULL    |                |
+-----------+---------------------+------+-----+---------+----------------+
6 rows in set (0.00 sec)

通過複製現存的表的表結構創建，但不複製數據  
MariaDB [hellodb]> create table newstudents2 like students;
Query OK, 0 rows affected (0.01 sec)

MariaDB [hellodb]> select * from newstudents2;   （這裡查看數據是沒有的）
Empty set (0.00 sec)

MariaDB [hellodb]> desc newstudents2;    （但是有表結構）
+-----------+---------------------+------+-----+---------+----------------+
| Field     | Type                | Null | Key | Default | Extra          |
+-----------+---------------------+------+-----+---------+----------------+
| StuID     | int(10) unsigned    | NO   | PRI | NULL    | auto_increment |
| Name      | varchar(50)         | NO   |     | NULL    |                |
| Age       | tinyint(3) unsigned | NO   |     | NULL    |                |
| Gender    | enum('F','M')       | NO   |     | NULL    |                |
| ClassID   | tinyint(3) unsigned | YES  |     | NULL    |                |
| TeacherID | int(10) unsigned    | YES  |     | NULL    |                |
+-----------+---------------------+------+-----+---------+----------------+
6 rows in set (0.00 sec)
  1. 表查看
查看支持的engine類型：
MariaDB [hellodb]> show engines;

+--------------------+---------+----------------------------------------------------------------------------------+--------------+------+------------+
| Engine             | Support | Comment                                                                          | Transactions | XA   | Savepoints |
+--------------------+---------+----------------------------------------------------------------------------------+--------------+------+------------+
| CSV                | YES     | Stores tables as CSV files                                                       | NO           | NO   | NO         |
| MRG_MyISAM         | YES     | Collection of identical MyISAM tables                                            | NO           | NO   | NO         |
| MyISAM             | YES     | Non-transactional engine with good performance and small data footprint          | NO           | NO   | NO         |
| SEQUENCE           | YES     | Generated tables filled with sequential values                                   | YES          | NO   | YES        |
| PERFORMANCE_SCHEMA | YES     | Performance Schema                                                               | NO           | NO   | NO         |
| MEMORY             | YES     | Hash based, stored in memory, useful for temporary tables                        | NO           | NO   | NO         |
| Aria               | YES     | Crash-safe tables with MyISAM heritage                                           | NO           | NO   | NO         |
| InnoDB             | DEFAULT | Supports transactions, row-level locking, foreign keys and encryption for tables | YES          | YES  | YES        |
+--------------------+---------+----------------------------------------------------------------------------------+--------------+------+------------+
8 rows in set (0.00 sec)

查看表：
MariaDB [hellodb]> show tables ;   （列出當前資料庫中的所有表）
+-------------------+
| Tables_in_hellodb |
+-------------------+
| classes           |
| coc               |
| courses           |
| newstudents       |
| newstudents2      |
| scores            |
| students          |
| teachers          |
| toc               |
+-------------------+
9 rows in set (0.00 sec)

MariaDB [hellodb]> show tables from mysql;   （指明資料庫查看這個資料庫的表）
+---------------------------+
| Tables_in_mysql           |
+---------------------------+
| column_stats              |
| columns_priv              |
| db                        |
| event                     |
| func                      |
| general_log               |
| gtid_slave_pos            |
| help_category             |
| help_keyword              |
| help_relation             |
| help_topic                |
| host                      |
| index_stats               |
| innodb_index_stats        |
| innodb_table_stats        |
| plugin                    |
| proc                      |
| procs_priv                |
| proxies_priv              |
| roles_mapping             |
| servers                   |
| slow_log                  |
| table_stats               |
| tables_priv               |
| time_zone                 |
| time_zone_leap_second     |
| time_zone_name            |
| time_zone_transition      |
| time_zone_transition_type |
| user                      |
+---------------------------+
30 rows in set (0.00 sec)

查看表結構：

MariaDB [hellodb]> desc students;
+-----------+---------------------+------+-----+---------+----------------+
| Field     | Type                | Null | Key | Default | Extra          |
+-----------+---------------------+------+-----+---------+----------------+
| StuID     | int(10) unsigned    | NO   | PRI | NULL    | auto_increment |
| Name      | varchar(50)         | NO   |     | NULL    |                |
| Age       | tinyint(3) unsigned | NO   |     | NULL    |                |
| Gender    | enum('F','M')       | NO   |     | NULL    |                |
| ClassID   | tinyint(3) unsigned | YES  |     | NULL    |                |
| TeacherID | int(10) unsigned    | YES  |     | NULL    |                |
+-----------+---------------------+------+-----+---------+----------------+

表結構欄位的意思。
1. Field:欄位表示的是別名
2. Type:欄位表示的是列的數據類型
3. Null :欄位表示這個列是否能取空值
4. Key :在mysql中key 和index 是一樣的意思，這個Key列可能會看到有如下的值：PRI(主鍵)、MUL(普通的b-tree索引)、UNI(唯一索引)
5. Default: 列的預設值
6. Extra :其它信息

查看指定表的創建命令：  （既創建過程）
MariaDB [hellodb]> show create table students;
+----------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Table    | Create Table                                                                                                                                                                                                                                                                                                                                                    |
+----------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| students | CREATE TABLE `students` (
  `StuID` int(10) unsigned NOT NULL AUTO_INCREMENT,
  `Name` varchar(50) NOT NULL,
  `Age` tinyint(3) unsigned NOT NULL,
  `Gender` enum('F','M') NOT NULL,
  `ClassID` tinyint(3) unsigned DEFAULT NULL,
  `TeacherID` int(10) unsigned DEFAULT NULL,
  PRIMARY KEY (`StuID`)
) ENGINE=InnoDB AUTO_INCREMENT=26 DEFAULT CHARSET=utf8 |
+----------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)

查看看表的狀態：（查看指定某個表狀態要加單引號）
MariaDB [hellodb]> SHOW TABLE STATUS LIKE 'students'\G; 
*************************** 1. row ***************************
           Name: students
         Engine: InnoDB
        Version: 10
     Row_format: Dynamic
           Rows: 25
 Avg_row_length: 655
    Data_length: 16384
Max_data_length: 0
   Index_length: 0
      Data_free: 0
 Auto_increment: 26
    Create_time: 2019-11-20 21:19:51
    Update_time: NULL
     Check_time: NULL
      Collation: utf8_general_ci
       Checksum: NULL
 Create_options: 
        Comment: 
1 row in set (0.00 sec)

查看庫中所有表的狀態：
MariaDB [hellodb]> show table status from hellodb\G;
*************************** 1. row ***************************
           Name: classes
         Engine: InnoDB
        Version: 10
     Row_format: Dynamic
           Rows: 8
 Avg_row_length: 2048
    Data_length: 16384
Max_data_length: 0
   Index_length: 0
      Data_free: 0
 Auto_increment: 9
    Create_time: 2019-11-20 21:19:51
    Update_time: NULL
     Check_time: NULL
      Collation: utf8_general_ci
       Checksum: NULL
 Create_options: 
        Comment: 
*************************** 2. row ***************************
           Name: coc
         Engine: InnoDB
        Version: 10
     Row_format: Dynamic
           Rows: 14
 Avg_row_length: 1170
    Data_length: 16384
Max_data_length: 0
   Index_length: 0
      Data_free: 0
 Auto_increment: 15
    Create_time: 2019-11-20 21:19:51
    Update_time: NULL
     Check_time: NULL
      Collation: utf8_general_ci
       Checksum: NULL
 Create_options: 
        Comment: 
.
.
.(省略證明我不是來混行數的)
.
.
*************************** 8. row ***************************
           Name: teachers
         Engine: InnoDB   （這裡是使用什麼存儲引擎的意思）
        Version: 10
     Row_format: Dynamic
           Rows: 4
 Avg_row_length: 4096
    Data_length: 16384
Max_data_length: 0
   Index_length: 0
      Data_free: 0
 Auto_increment: 5
    Create_time: 2019-11-20 21:19:51
    Update_time: NULL
     Check_time: NULL
      Collation: utf8_general_ci
       Checksum: NULL
 Create_options: 
        Comment: 
*************************** 9. row ***************************
           Name: toc
         Engine: InnoDB
        Version: 10
     Row_format: Dynamic
           Rows: 0
 Avg_row_length: 0
    Data_length: 16384
Max_data_length: 0
   Index_length: 0
      Data_free: 0
 Auto_increment: 1
    Create_time: 2019-11-20 21:19:51
    Update_time: NULL
     Check_time: NULL
      Collation: utf8_general_ci
       Checksum: NULL
 Create_options: 
        Comment: 
9 rows in set (0.00 sec)
  1. 修改刪除表
刪除表：
MariaDB [hellodb]> show tables;
+-------------------+
| Tables_in_hellodb |
+-------------------+
| classes           |
| coc               |
| courses           |
| newstudents       |
| newstudents2      |
| scores            |
| students          |
| students2         |
| teachers          |
| toc               |
+-------------------+
10 rows in set (0.00 sec)

MariaDB [hellodb]> drop table newstudents2;
Query OK, 0 rows affected (0.00 sec)

MariaDB [hellodb]> show tables;
+-------------------+
| Tables_in_hellodb |
+-------------------+
| classes           |
| coc               |
| courses           |
| newstudents       |
| scores            |
| students          |
| students2         |
| teachers          |
| toc               |
+-------------------+
9 rows in set (0.00 sec)

查看修改表幫助：
MariaDB [hellodb]> help ALTER TABLE
Name: 'ALTER TABLE'
Description:
Syntax:
ALTER [ONLINE | OFFLINE] [IGNORE] TABLE tbl_name
    [alter_specification [, alter_specification] ...]
    [partition_options]

修改表：
MariaDB [hellodb]> show tables;
+-------------------+
| Tables_in_hellodb |
+-------------------+
| classes           |
| coc               |
| courses           |
| scores            |
| students          |
| teachers          |
| toc               |
+-------------------+
7 rows in set (0.00 sec)

MariaDB [hellodb]> alter table students rename s1;   （修改表名為s1）
Query OK, 0 rows affected (0.00 sec)

MariaDB [hellodb]> select * from students;
ERROR 1146 (42S02): Table 'hellodb.students' doesn't exist
MariaDB [hellodb]> show tables;
+-------------------+
| Tables_in_hellodb |
+-------------------+
| classes           |
| coc               |
| courses           |
| s1                |
| scores            |
| teachers          |
| toc               |
+-------------------+
7 rows in set (0.00 sec)

MariaDB [hellodb]> alter table s1 add phone varchar(11) after name; （在name欄位後面添加phone欄位）  ADD：添加欄位   varchar可變的 字元長度為11為
Query OK, 0 rows affected (0.01 sec)
Records: 0  Duplicates: 0  Warnings: 0

MariaDB [hellodb]> select * from s1;
+-------+---------------+-------+-----+--------+---------+-----------+
| StuID | Name          | phone | Age | Gender | ClassID | TeacherID |
+-------+---------------+-------+-----+--------+---------+-----------+
|     1 | Shi Zhongyu   | NULL  |  22 | M      |       2 |         3 |
|     2 | Shi Potian    | NULL  |  22 | M      |       1 |         7 |
|     3 | Xie Yanke     | NULL  |  53 | M      |       2 |        16 |
|     4 | Ding Dian     | NULL  |  32 | M      |       4 |         4 |
|     5 | Yu Yutong     | NULL  |  26 | M      |       3 |         1 |
|     6 | Shi Qing      | NULL  |  46 | M      |       5 |      NULL |
|     7 | Xi Ren        | NULL  |  19 | F      |       3 |      NULL |
|     8 | Lin Daiyu     | NULL  |  17 | F      |       7 |      NULL |
|     9 | Ren Yingying  | NULL  |  20 | F      |       6 |      NULL |
|    10 | Yue Lingshan  | NULL  |  19 | F      |       3 |      NULL |
|    11 | Yuan Chengzhi | NULL  |  23 | M      |       6 |      NULL |
|    12 | Wen Qingqing  | NULL  |  19 | F      |       1 |      NULL |
|    13 | Tian Boguang  | NULL  |  33 | M      |       2 |      NULL |
|    14 | Lu Wushuang   | NULL  |  17 | F      |       3 |      NULL |
|    15 | Duan Yu       | NULL  |  19 | M      |       4 |      NULL |
|    16 | Xu Zhu        | NULL  |  21 | M      |       1 |      NULL |
|    17 | Lin Chong     | NULL  |  25 | M      |       4 |      NULL |
|    18 | Hua Rong      | NULL  |  23 | M      |       7 |      NULL |
|    19 | Xue Baochai   | NULL  |  18 | F      |       6 |      NULL |
|    20 | Diao Chan     | NULL  |  19 | F      |       7 |      NULL |
|    21 | Huang Yueying | NULL  |  22 | F      |       6 |      NULL |
|    22 | Xiao Qiao     | NULL  |  20 | F      |       1 |      NULL |
|    23 | Ma Chao       | NULL  |  23 | M      |       4 |      NULL |
|    24 | Xu Xian       | NULL  |  27 | M      |    NULL |      NULL |
|    25 | Sun Dasheng   | NULL  | 100 | M      |    NULL |      NULL |
+-------+---------------+-------+-----+--------+---------+-----------+
25 rows in set (0.00 sec)

MariaDB [hellodb]> alter table s1 modify phone int;  （把phone的數據類型改為int）
Query OK, 25 rows affected (0.01 sec)              
Records: 25  Duplicates: 0  Warnings: 0

MariaDB [hellodb]> desc s1
    -> ;
+-----------+---------------------+------+-----+---------+----------------+
| Field     | Type                | Null | Key | Default | Extra          |
+-----------+---------------------+------+-----+---------+----------------+
| StuID     | int(10) unsigned    | NO   | PRI | NULL    | auto_increment |
| Name      | varchar(50)         | NO   |     | NULL    |                |
| phone     | int(11)             | YES  |     | NULL    |                |
| Age       | tinyint(3) unsigned | NO   |     | NULL    |                |
| Gender    | enum('F','M')       | NO   |     | NULL    |                |
| ClassID   | tinyint(3) unsigned | YES  |     | NULL    |                |
| TeacherID | int(10) unsigned    | YES  |     | NULL    |                |
+-----------+---------------------+------+-----+---------+----------------+
7 rows in set (0.00 sec)

（這些就不一一解釋了有興趣的可以自己試一試）
ALTER TABLE s1 CHANGE COLUMN phone mobile char(11);
ALTER TABLE s1 DROP COLUMN mobile;
ALTER TABLE s1 character set utf8;
ALTER TABLE s1 change name name varchar(20) character set utf8;
ALTER TABLE students ADD gender ENUM('m','f');
ALETR TABLE students CHANGE id sid int UNSIGNED NOT NULL PRIMARY KEY;
ALTER TABLE students drop primary key ;
ALTER TABLE students drop primary key ;
DESC students;
ALTER TABLE students DROP age;

DML語句

DML: INSERT, DELETE, UPDATE

INSERT 語句
功能：一次插入一行或多行數據 語法

UPDATE 語句
語句用於修改表中的數據。 註意：一定要有限制條件，否則將修改所有行的指定欄位

DELETE語句
語句用於刪除表中的行。 註意：一定要有限制條件，否則將清空表中的所有數據
可以在不刪除表的情況下刪除所有的行。這意味著表的結構、屬性和索引都是完整的：
DELETE FROM table_name 或者 DELETE * FROM table_name
  1. INSERT語句實驗: 三種語句
MariaDB [hellodb]> help insert;
Name: 'INSERT'
Description:
Syntax:
INSERT [LOW_PRIORITY | DELAYED | HIGH_PRIORITY] [IGNORE]
    [INTO] tbl_name [(col_name,...)]
    {VALUES | VALUE} ({expr | DEFAULT},...),(...),...
    [ ON DUPLICATE KEY UPDATE
      col_name=expr
        [, col_name=expr] ... ]

Or:

INSERT [LOW_PRIORITY | DELAYED | HIGH_PRIORITY] [IGNORE]
    [INTO] tbl_name
    SET col_name={expr | DEFAULT}, ...
    [ ON DUPLICATE KEY UPDATE
      col_name=expr
        [, col_name=expr] ... ]

Or:

INSERT [LOW_PRIORITY | HIGH_PRIORITY] [IGNORE]
    [INTO] tbl_name [(col_name,...)]
    SELECT ...
    [ ON DUPLICATE KEY UPDATE
      col_name=expr
        [, col_name=expr] ... ]
  • 第一種語法
MariaDB [hellodb]> insert into s1 values(26,'xietingfeng',NULL,23,'M',2,1); (添加一行表記錄) 
Query OK, 1 row affected (0.00 sec)

MariaDB [hellodb]> select * from s1;
+-------+---------------+-------+-----+--------+---------+-----------+
| StuID | Name          | phone | Age | Gender | ClassID | TeacherID |
+-------+---------------+-------+-----+--------+---------+-----------+
|     1 | Shi Zhongyu   |  NULL |  22 | M      |       2 |         3 |
|     2 | Shi Potian    |  NULL |  22 | M      |       1 |         7 |
|     3 | Xie Yanke     |  NULL |  53 | M      |       2 |        16 |
|     4 | Ding Dian     |  NULL |  32 | M      |       4 |         4 |
|     5 | Yu Yutong     |  NULL |  26 | M      |       3 |         1 |
|     6 | Shi Qing      |  NULL |  46 | M      |       5 |      NULL |
|     7 | Xi Ren        |  NULL |  19 | F      |       3 |      NULL |
|     8 | Lin Daiyu     |  NULL |  17 | F      |       7 |      NULL |
|     9 | Ren Yingying  |  NULL |  20 | F      |       6 |      NULL |
|    10 | Yue Lingshan  |  NULL |  19 | F      |       3 |      NULL |
|    11 | Yuan Chengzhi |  NULL |  23 | M      |       6 |      NULL |
|    12 | Wen Qingqing  |  NULL |  19 | F      |       1 |      NULL |
|    13 | Tian Boguang  |  NULL |  33 | M      |       2 |      NULL |
|    14 | Lu Wushuang   |  NULL |  17 | F      |       3 |      NULL |
|    15 | Duan Yu       |  NULL |  19 | M      |       4 |      NULL |
|    16 | Xu Zhu        |  NULL |  21 | M      |       1 |      NULL |
|    17 | Lin Chong     |  NULL |  25 | M      |       4 |      NULL |
|    18 | Hua Rong      |  NULL |  23 | M      |       7 |      NULL |
|    19 | Xue Baochai   |  NULL |  18 | F      |       6 |      NULL |
|    20 | Diao Chan     |  NULL |  19 | F      |       7 |      NULL |
|    21 | Huang Yueying |  NULL |  22 | F      |       6 |      NULL |
|    22 | Xiao Qiao     |  NULL |  20 | F      |       1 |      NULL |
|    23 | Ma Chao       |  NULL |  23 | M      |       4 |      NULL |
|    24 | Xu Xian       |  NULL |  27 | M      |    NULL |      NULL |
|    25 | Sun Dasheng   |  NULL | 100 | M      |    NULL |      NULL |
|    26 | xietingfeng   |  NULL |  23 | M      |       2 |         1 |
+-------+---------------+-------+-----+--------+---------+-----------+
26 rows in set (0.00 sec)

（如果出現這個提示可能是你少寫了一個欄位或者寫錯了）
MariaDB [hellodb]> insert into s1 values(26,'xietingfeng',23,'M',2,1);
ERROR 1136 (21S01): Column count doesn't match value count at row 1

註意：如果想省略欄位名的話，只能所有欄位都賦值的話可以省略，單個賦值不可以省略。
如下：挑出三個欄位來賦值，必須對應的寫上。
MariaDB [hellodb]> insert into s1(name,age,classid) values ('liudehua',18,1);
Query OK, 1 row affected (0.00 sec)

MariaDB [hellodb]> select * from s1;
+-------+---------------+-------+-----+--------+---------+-----------+
| StuID | Name          | phone | Age | Gender | ClassID | TeacherID |
+-------+---------------+-------+-----+--------+---------+-----------+
|     1 | Shi Zhongyu   |  NULL |  22 | M      |       2 |         3 |
|     2 | Shi Potian    |  NULL |  22 | M      |       1 |         7 |
|     3 | Xie Yanke     |  NULL |  53 | M      |       2 |        16 |
|     4 | Ding Dian     |  NULL |  32 | M      |       4 |         4 |
|     5 | Yu Yutong     |  NULL |  26 | M      |       3 |         1 |
|     6 | Shi Qing      |  NULL |  46 | M      |       5 |      NULL |
|     7 | Xi Ren        |  NULL |  19 | F      |       3 |      NULL |
|     8 | Lin Daiyu     |  NULL |  17 | F      |       7 |      NULL |
|     9 | Ren Yingying  |  NULL |  20 | F      |       6 |      NULL |
|    10 | Yue Lingshan  |  NULL |  19 | F      |       3 |      NULL |
|    11 | Yuan Chengzhi |  NULL |  23 | M      |       6 |      NULL |
|    12 | Wen Qingqing  |  NULL |  19 | F      |       1 |      NULL |
|    13 | Tian Boguang  |  NULL |  33 | M      |       2 |      NULL |
|    14 | Lu Wushuang   |  NULL |  17 | F      |       3 |      NULL |
|    15 | Duan Yu       |  NULL |  19 | M      |       4 |      NULL |
|    16 | Xu Zhu        |  NULL |  21 | M      |       1 |      NULL |
|    17 | Lin Chong     |  NULL |  25 | M      |       4 |      NULL |
|    18 | Hua Rong      |  NULL |  23 | M      |       7 |      NULL |
|    19 | Xue Baochai   |  NULL |  18 | F      |       6 |      NULL |
|    20 | Diao Chan     |  NULL |  19 | F      |       7 |      NULL |
|    21 | Huang Yueying |  NULL |  22 | F      |       6 |      NULL |
|    22 | Xiao Qiao     |  NULL |  20 | F      |       1 |      NULL |
|    23 | Ma Chao       |  NULL |  23 | M      |       4 |      NULL |
|    24 | Xu Xian       |  NULL |  27 | M      |    NULL |      NULL |
|    25 | Sun Dasheng   |  NULL | 100 | M      |    NULL |      NULL |
|    26 | xietingfeng   |  NULL |  23 | M      |       2 |         1 |
|    27 | liudehua      |  NULL |  18 | F      |       1 |      NULL |
+-------+---------------+-------+-----+--------+---------+-----------+
27 rows in set (0.00 sec)              （↑ 這裡是因為表結構設置預設不允許為空隨機分配的值）

一次行兩條記錄賦值：
MariaDB [hellodb]> insert into s1(name,age,gender,classid) values('mahuateng',20,'M',3),('wuyanzu',19,'M',4);
Query OK, 2 rows affected (0.00 sec)
Records: 2  Duplicates: 0  Warnings: 0

MariaDB [hellodb]> select * from s1;
+-------+---------------+-------+-----+--------+---------+-----------+
| StuID | Name          | phone | Age | Gender | ClassID | TeacherID |
+-------+---------------+-------+-----+--------+---------+-----------+
|     1 | Shi Zhongyu   |  NULL |  22 | M      |       2 |         3 |
|     2 | Shi Potian    |  NULL |  22 | M      |       1 |         7 |
|     3 | Xie Yanke     |  NULL |  53 | M      |       2 |        16 |
|     4 | Ding Dian     |  NULL |  32 | M      |       4 |         4 |
|     5 | Yu Yutong     |  NULL |  26 | M      |       3 |         1 |
|     6 | Shi Qing      |  NULL |  46 | M      |       5 |      NULL |
|     7 | Xi Ren        |  NULL |  19 | F      |       3 |      NULL |
|     8 | Lin Daiyu     |  NULL |  17 | F      |       7 |      NULL |
|     9 | Ren Yingying  |  NULL |  20 | F      |       6 |      NULL |
|    10 | Yue Lingshan  |  NULL |  19 | F      |       3 |      NULL |
|    11 | Yuan Chengzhi |  NULL |  23 | M      |       6 |      NULL |
|    12 | Wen Qingqing  |  NULL |  19 | F      |       1 |      NULL |
|    13 | Tian Boguang  |  NULL |  33 | M      |       2 |      NULL |
|    14 | Lu Wushuang   |  NULL |  17 | F      |       3 |      NULL |
|    15 | Duan Yu       |  NULL |  19 | M      |       4 |      NULL |
|    16 | Xu Zhu        |  NULL |  21 | M      |       1 |      NULL |
|    17 | Lin Chong     |  NULL |  25 | M      |       4 |      NULL |
|    18 | Hua Rong      |  NULL |  23 | M      |       7 |      NULL |
|    19 | Xue Baochai   |  NULL |  18 | F      |       6 |      NULL |
|    20 | Diao Chan     |  NULL |  19 | F      |       7 |      NULL |
|    21 | Huang Yueying |  NULL |  22 | F      |       6 |      NULL |
|    22 | Xiao Qiao     |  NULL |  20 | F      |       1 |      NULL |
|    23 | Ma Chao       |  NULL |  23 | M      |       4 |      NULL |
|    24 | Xu Xian       |  NULL |  27 | M      |    NULL |      NULL |
|    25 | Sun Dasheng   |  NULL | 100 | M      |    NULL |      NULL |
|    26 | xietingfeng   |  NULL |  23 | M      |       2 |         1 |
|    27 | liudehua      |  NULL |  18 | F      |       1 |      NULL |
|    28 | mahuateng     |  NULL |  20 | M      |       3 |      NULL |
|    29 | wuyanzu       |  NULL |  19 | M      |       4 |      NULL |
+-------+---------------+-------+-----+--------+---------+-----------+
29 rows in set (0.00 sec)
  • 第二種語法
MariaDB [hellodb]> insert s1 set name='wuzetian',age=21,gender='F';
Query OK, 1 row affected (0.00 sec)

MariaDB [hellodb]> select * from s1;
+-------+---------------+-------+-----+--------+---------+-----------+
| StuID | Name          | phone | Age | Gender | ClassID | TeacherID |
+-------+---------------+-------+-----+--------+---------+-----------+
|     1 | Shi Zhongyu   |  NULL |  22 | M      |       2 |         3 |
|     2 | Shi Potian    |  NULL |  22 | M      |       1 |         7 |
|     3 | Xie Yanke     |  NULL |  53 | M      |       2 |        16 |
|     4 | Ding Dian     |  NULL |  32 | M      |       4 |         4 |
|     5 | Yu Yutong     |  NULL |  26 | M      |       3 |         1 |
|     6 | Shi Qing      |  NULL |  46 | M      |       5 |      NULL |
|     7 | Xi Ren        |  NULL |  19 | F      |       3 |      NULL |
|     8 | Lin Daiyu     |  NULL |  17 | F      |       7 |      NULL |
|     9 | Ren Yingying  |  NULL |  20 | F      |       6 |      NULL |
|    10 | Yue Lingshan  |  NULL |  19 | F      |       3 |      NULL |
|    11 | Yuan Chengzhi |  NULL |  23 | M      |       6 |      NULL |
|    12 | Wen Qingqing  |  NULL |  19 | F      |       1 |      NULL |
|    13 | Tian Boguang  |  NULL |  33 | M      |       2 |      NULL |
|    14 | Lu Wushuang   |  NULL |  17 | F      |       3 |      NULL |
|    15 | Duan Yu       |  NULL |  19 | M      |       4 |      NULL |
|    16 | Xu Zhu        |  NULL |  21 | M      |       1 |      NULL |
|    17 | Lin Chong     |  NULL |  25 | M      |       4 |      NULL |
|    18 | Hua Rong      |  NULL |  23 | M      |       7 |      NULL |
|    19 | Xue Baochai   |  NULL |  18 | F      |       6 |      NULL |
|    20 | Diao Chan     |  NULL |  19 | F      |       7 |      NULL |
|    21 | Huang Yueying |  NULL |  22 | F      |       6 |      NULL |
|    22 | Xiao Qiao     |  NULL |  20 | F      |       1 |      NULL |
|    23 | Ma Chao       |  NULL |  23 | M      |       4 |      NULL |
|    24 | Xu Xian       |  NULL |  27 | M      |    NULL |      NULL |
|    25 | Sun Dasheng   |  NULL | 100 | M      |    NULL |      NULL |
|    26 | xietingfeng   |  NULL |  23 | M      |       2 |         1 |
|    27 | liudehua      |  NULL |  18 | F      |       1 |      NULL |
|    28 | mahuateng     |  NULL |  20 | M      |       3 |      NULL |
|    29 | wuyanzu       |  NULL |  19 | M      |       4 |      NULL |
|    30 | wuzetian      |  NULL |  21 | F      |    NULL |      NULL |
+-------+---------------+-------+-----+--------+---------+-----------+
30 rows in set (0.00 sec)
(使用的不多一般使用第一種瞭解一下)
  • 第三種語法
MariaDB [hellodb]> select * from teachers;
+-----+---------------+-----+--------+
| TID | Name          | Age | Gender |
+-----+---------------+-----+--------+
|   1 | Song Jiang    |  45 | M      |
|   2 | Zhang Sanfeng |  94 | M      |
|   3 | Miejue Shitai |  77 | F      |
|   4 | Lin Chaoying  |  93 | F      |
+-----+---------------+-----+--------+
4 rows in set (0.00 sec)

MariaDB [hellodb]> insert s1 (name,classid,gender,age) select name,age,gender,18 from teachers;
Query OK, 4 rows affected (0.00 sec)
Records: 4  Duplicates: 0  Warnings: 0

MariaDB [hellodb]> select * from s1;
+-------+---------------+-------+-----+--------+---------+-----------+
| StuID | Name          | phone | Age | Gender | ClassID | TeacherID |
+-------+---------------+-------+-----+--------+---------+-----------+
|     1 | Shi Zhongyu   |  NULL |  22 | M      |       2 |         3 |
|     2 | Shi Potian    |  NULL |  22 | M      |       1 |         7 |
|     3 | Xie Yanke     |  NULL |  53 | M      |       2 |        16 |
|     4 | Ding Dian     |  NULL |  32 | M      |       4 |         4 |
|     5 | Yu Yutong     |  NULL |  26 | M      |       3 |         1 |
|     6 | Shi Qing      |  NULL |  46 | M      |       5 |      NULL |
|     7 | Xi Ren        |  NULL |  19 | F      |       3 |      NULL |
|     8 | Lin Daiyu     |  NULL |  17 | F      |       7 |      NULL |
|     9 | Ren Yingying  |  NULL |  20 | F      |       6 |      NULL |
|    10 | Yue Lingshan  |  NULL |  19 | F      |       3 |      NULL |
|    11 | Yuan Chengzhi |  NULL |  23 | M      |       6 |      NULL |
|    12 | Wen Qingqing  |  NULL |  19 | F      |       1 |      NULL |
|    13 | Tian Boguang  |  NULL |  33 | M      |       2 |      NULL |
|    14 | Lu Wushuang   |  NULL |  17 | F      |       3 |      NULL |
|    15 | Duan Yu       |  NULL |  19 | M      |       4 |      NULL |
|    16 | Xu Zhu        |  NULL |  21 | M      |       1 |      NULL |
|    17 | Lin Chong     |  NULL |  25 | M      |       4 |      NULL |
|    18 | Hua Rong      |  NULL |  23 | M      |       7 |      NULL |
|    19 | Xue Baochai   |  NULL |  18 | F      |       6 |      NULL |
|    20 | Diao Chan     |  NULL |  19 | F      |       7 |      NULL |
|    21 | Huang Yueying |  NULL |  22 | F      |       6 |      NULL |
|    22 | Xiao Qiao     |  NULL |  20 | F      |       1 |      NULL |
|    23 | Ma Chao       |  NULL |  23 | M      |       4 |      NULL |
|    24 | Xu Xian       |  NULL |  27 | M      |    NULL |      NULL |
|    25 | Sun Dasheng   |  NULL | 100 | M      |    NULL |      NULL |
|    26 | xietingfeng   |  NULL |  23 | M      |       2 |         1 |
|    27 | liudehua      |  NULL |  18 | F      |       1 |      NULL |
|    28 | mahuateng     |  NULL |  20 | M      |       3 |      NULL |
|    29 | wuyanzu       |  NULL |  19 | M      |       4 |      NULL |
|    30 | wuzetian      |  NULL |  21 | F      |    NULL |      NULL |
|    31 | Song Jiang    |  NULL |  18 | M      |      45 |      NULL |
|    32 | Zhang Sanfeng |  NULL |  18 | M      |      94 |      NULL |
|    33 | Miejue Shitai |  NULL |  18 | F      |      77 |      NULL |
|    34 | Lin Chaoying  |  NULL |  18 | F      |      93 |      NULL |
+-------+---------------+-------+-----+--------+---------+-----------+
34 rows in set (0.00 sec)
（批量導入，A表參考B表的結構導入到B表中，主鍵必須是唯一的不可導入A表的主鍵）
  1. UPDATE語句
MariaDB [hellodb]> help update;  (語句幫助)
Name: 'UPDATE'
Description:
Syntax:
Single-table syntax:

UPDATE [LOW_PRIORITY] [IGNORE] table_reference
    SET col_name1={expr1|DEFAULT} [, col_name2={expr2|DEFAULT}] ...
    [WHERE where_condition]
    [ORDER BY ...]
    [LIMIT row_count]

MariaDB [hellodb]> select * from n1;  （不加指定修改會把整個列都修改）
+-------+---------------+-------+-----+--------+---------+-----------+
| StuID | Name          | phone | Age | Gender | ClassID | TeacherID |
+-------+---------------+-------+-----+--------+---------+-----------+
|     1 | Shi Zhongyu   |  NULL |  22 | M      |       2 |         3 |
|     2 | Shi Potian    |  NULL |  22 | M      |       1 |         7 |
|     3 | Xie Yanke     |  NULL |  53 | M      |       2 |        16 |
|     4 | Ding Dian     |  NULL |  32 | M      |       4 |         4 |
|     5 | Yu Yutong     |  NULL |  26 | M      |       3 |         1 |
|     6 | Shi Qing      |  NULL |  46 | M      |       5 |      NULL |
|     7 | Xi Ren        |  NULL |  19 | F      |       3 |      NULL |
|     8 | Lin Daiyu     |  NULL |  17 | F      |       7 |      NULL |
|     9 | Ren Yingying  |  NULL |  20 | F      |       6 |      NULL |
|    10 | Yue Lingshan  |  NULL |  19 | F      |       3 |      NULL |
|    11 | Yuan Chengzhi |  NULL |  23 | M      |       6 |      NULL |
|    12 | Wen Qingqing  |  NULL |  19 | F      |       1 |      NULL |
|    13 | Tian Boguang  |  NULL |  33 | M      |       2 |      NULL |
|    14 | Lu Wushuang   |  NULL |  17 | F      |       3 |      NULL |
|    15 | Duan Yu       |  NULL |  19 | M      |       4 |      NULL |
|    16 | Xu Zhu        |  NULL |  21 | M      |       1 |      NULL |
|    17 | Lin Chong     |  NULL |  25 | M      |       4 |      NULL |
|    18 | Hua Rong      |  NULL |  23 | M      |       7 |      NULL |
|    19 | Xue Baochai   |  NULL |  18 | F      |       6 |      NULL |
|    20 | Diao Chan     |  NULL |  19 | F      |       7 |      NULL |
|    21 | Huang Yueying |  NULL |  22 | F      |       6 |      NULL |
|    22 | Xiao Qiao     |  NULL |  20 | F      |       1 |      NULL |
|    23 | Ma Chao       |  NULL |  23 | M      |       4 |      NULL |
|    24 | Xu Xian       |  NULL |  27 | M      |    NULL |      NULL |
|    25 | Sun Dasheng   |  NULL | 100 | M      |    NULL |      NULL |
|    26 | xietingfeng   |  NULL |  23 | M      |       2 |         1 |
|    27 | liudehua      |  NULL |  18 | F      |       1 |      NULL |
|    28 | mahuateng     |  NULL |  20 | M      |       3 |      NULL |
|    29 | wuyanzu       |  NULL |  19 | M      |       4 |      NULL |
|    30 | wuzetian      |  NULL |  21 | F      |    NULL |      NULL |
|    31 | Song Jiang    |  NULL |  18 | M      |      45 |      NULL |
|    32 | Zhang Sanfeng |  NULL |  18 | M      |      94 |      NULL |
|    33 | Miejue Shitai |  NULL |  18 | F      |      77 |      NULL |
|    34 | Lin Chaoying  |  NULL |  18 | F      |      93 |      NULL |
+-------+---------------+-------+-----+--------+---------+-----------+
34 rows in set (0.00 sec)

MariaDB [hellodb]> update n1 set teacherid=1; 
Query OK, 32 rows affected (0.00 sec)
Rows matched: 34  Changed: 32  Warnings: 0

MariaDB [hellodb]> select * from n1;
+-------+---------------+-------+-----+--------+---------+-----------+
| StuID | Name          | phone | Age | Gender | ClassID | TeacherID |
+-------+---------------+-------+-----+--------+---------+-----------+
|     1 | Shi Zhongyu   |  NULL |  22 | M      |       2 |         1 |
|     2 | Shi Potian    |  NULL |  22 | M      |       1 |         1 |
|     3 | Xie Yanke     |  NULL |  53 | M      |       2 |         1 |
|     4 | Ding Dian     |  NULL |  32 | M      |       4 |         1 |
|     5 | Yu Yutong     |  NULL |  26 | M      |       3 |         1 |
|     6 | Shi Qing      |  NULL |  46 | M      |       5 |         1 |
|     7 | Xi Ren        |  NULL |  19 | F      |       3 |         1 |
|     8 | Lin Daiyu     |  NULL |  17 | F      |       7 |         1 |
|     9 | Ren Yingying  |  NULL |  20 | F      |       6 |         1 |
|    10 | Yue Lingshan  |  NULL |  19 | F      |       3 |         1 |
|    11 | Yuan Chengzhi |  NULL |  23 | M      |       6 |         1 |
|    12 | Wen Qingqing  |  NULL |  19 | F      |       1 |         1 |
|    13 | Tian Boguang  |  NULL |  33 | M      |       2 |         1 |
|    14 | Lu Wushuang   |  NULL |  17 | F      |       3 |         1 |
|    15 | Duan Yu       |  NULL |  19 | M      |       4 |         1 |
|    16 | Xu Zhu        |  NULL |  21 | M      |       1 |         1 |
|    17 | Lin Chong     |  NULL |  25 | M      |       4 |         1 |
|    18 | Hua Rong      |  NULL |  23 | M      |       7 |         1 |
|    19 | Xue Baochai   |  NULL |  18 | F      |       6 |         1 |
|    20 | Diao Chan     |  NULL |  19 | F      |       7 |         1 |
|    21 | Huang Yueying |  NULL |  22 | F      |       6 |         1 |
|    22 | Xiao Qiao     |  NULL |  20 | F      |       1 |         1 |
|    23 | Ma Chao       |  NULL |  23 | M      |       4 |         1 |
|    24 | Xu Xian       |  NULL |  27 | M      |    NULL |         1 |
|    25 | Sun Dasheng   |  NULL | 100 | M      |    NULL |         1 |
|    26 | xietingfeng   |  NULL |  23 | M      |       2 |         1 |
|    27 | liudehua      |  NULL |  18 | F      |       1 |         1 |
|    28 | mahuateng     |  NULL |  20 | M      |       3 |         1 |
|    29 | wuyanzu       |  NULL |  19 | M      |       4 |         1 |
|    30 | wuzetian      |  NULL |  21 | F      |    NULL |         1 |
|    31 | Song Jiang    |  NULL |  18 | M      |      45 |         1 |
|    32 | Zhang Sanfeng |  NULL |  18 | M      |      94 |         1 |
|    33 | Miejue Shitai |  NULL |  18 | F      |      77 |         1 |
|    34 | Lin Chaoying  |  NULL |  18 | F      |      93 |         1 |
+-------+---------------+-------+-----+--------+---------+-----------+
34 rows in set (0.00 sec)

避免的方法：登陸的時候加-U進入安全模式，改模式下不加where指定不能更改。
[root@centos7 ~]#mysql -U -uroot -p123456
Welcome to the MariaDB monitor.  Commands end with ; or \g.
Your MariaDB connection id is 11
Server version: 10.2.29-MariaDB-log MariaDB Server

Copyright (c) 2000, 2018, Oracle, MariaDB Corporation Ab and others.

Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.

MariaDB [(none)]> update n1 set teacherid=2;
ERROR 1046 (3D000): No database selected
MariaDB [(none)]> 

或者修改配文件： 在mysql下麵加上這一行
[root@centos7 ~]#vim /etc/my.cnf.d/mysql-clients.cnf
[mysql]
safe-updates

MariaDB [hellodb]> update n1 set teacherid=2 where stuid=25;  （用where指定主鍵的某一範圍修改）
Query OK, 1 row affected (0.00 sec)
Rows matched: 1  Changed: 1  Warnings: 0

MariaDB [hellodb]> select * from n1
    -> ;
+-------+---------------+-------+-----+--------+---------+-----------+
| stuid | Name          | phone | Age | Gender | ClassID | TeacherID |
+-------+---------------+-------+-----+--------+---------+-----------+
|     1 | Shi Zhongyu   |  NULL |  22 | M      |       2 |         1 |
|     2 | Shi Potian    |  NULL |  22 | M      |       1 |         1 |
|     3 | Xie Yanke     |  NULL |  53 | M      |       2 |         1 |
|     4 | Ding Dian     |  NULL |  32 | M      |       4 |         1 |
|     5 | Yu Yutong     |  NULL |  26 | M      |       3 |         1 |
|     6 | Shi Qing      |  NULL |  46 | M      |       5 |         1 |
|     7 | Xi Ren        |  NULL |  19 | F      |       3 |         1 |
|     8 | Lin Daiyu     |  NULL |  17 | F      |       7 |         1 |
|     9 | Ren Yingying  |  NULL |  20 | F      |       6 |         1 |
|    10 | Yue Lingshan  |  NULL |  19 | F      |       3 |         1 |
|    11 | Yuan Chengzhi |  NULL |  23 | M      |       6 |         1 |
|    12 | Wen Qingqing  |  NULL |  19 | F      |       1 |         1 |
|    13 | Tian Boguang  |  NULL |  33 | M      |       2 |         1 |
|    14 | Lu Wushuang   |  NULL |  17 | F      |       3 |         1 |
|    15 | Duan Yu       |  NULL |  19 | M      |       4 |         1 |
|    16 | Xu Zhu        |  NULL |  21 | M      |       1 |         1 |
|    17 | Lin Chong     |  NULL |  25 | M      |       4 |         1 |
|    18 | Hua Rong      |  NULL |  23 | M      |       7 |         1 |
|    19 | Xue Baochai   |  NULL |  18 | F      |       6 |         1 |
|    20 | Diao Chan     |  NULL |  19 | F      |       7 |         1 |
|    21 | Huang Yueying |  NULL |  22 | F      |       6 |         1 |
|    22 | Xiao Qiao     |  NULL |  20 | F      |       1 |         1 |
|    23 | Ma Chao       |  NULL |  23 | M      |       4 |         1 |
|    24 | Xu Xian       |  NULL |  27 | M      |    NULL |         1 |
|    25 | Sun Dasheng   |  NULL | 100 | M      |    NULL |         2 |
|    26 | xietingfeng   |  NULL |  23 | M      |       2 |         1 |
|    27 | liudehua      |  NULL |  18 | F      |       1 |         1 |
|    28 | mahuateng     |  NULL |  20 | M      |       3 |         1 |
|    29 | wuyanzu       |  NULL |  19 | M      |       4 |         1 |
|    30 | wuzetian      |  NULL |  21 | F      |    NULL |         1 |
|    31 | Song Jiang    |  NULL |  18 | M      |      45 |         1 |
|    32 | Zhang Sanfeng |  NULL |  18 | M      |      94 |         1 |
|    33 | Miejue Shitai |  NULL |  18 | F      |      77 |         1 |
|    34 | Lin Chaoying  |  NULL |  18 | F      |      93 |         1 |
+-------+---------------+-------+-----+--------+---------+-----------+
34 rows in set (0.00 sec)
註意：安全模式下，這樣修改表必須有主鍵才可以修改。

添加主鍵方法：
MariaDB [hellodb]> alter table n1 change stuid stuid int primary key;
  1. DELETE語句：（也要加where） （-U 和配置文件修改都支持）
MariaDB [hellodb]> delete from n1 where stuid=28;  （刪除這一行）
Query OK, 1 row affected (0.00 sec)

MariaDB [hellodb]> select * from n1; 
+-------+---------------+-------+-----+--------+---------+-----------+
| stuid | Name          | phone | Age | Gender | ClassID | TeacherID |
+-------+---------------+-------+-----+--------+---------+-----------+

|    24 | Xu Xian       |  NULL |  27 | M      |    NULL |         1 |
|    25 | Sun Dasheng   |  NULL | 100 | M      |    NULL |         2 |
|    26 | xietingfeng   |  NULL |  23 | M      |       2 |         1 |
|    27 | liudehua      |  NULL |  18 | F      |       1 |         1 |
|    29 | wuyanzu       |  NULL |  19 | M      |       4 |         1 |
|    30 | wuzetian      |  NULL |  21 | F      |    NULL |         1 |
|    31 | Song Jiang    |  NULL |  18 | M      |      45 |         1 |
|    32 | Zhang Sanfeng |  NULL |  18 | M      |      94 |         1 |
|    33 | Miejue Shitai |  NULL |  18 | F      |      77 |         1 |
|    34 | Lin Chaoying  |  NULL |  18 | F      |      93 |         1 |
+-------+---------------+-------+-----+--------+---------+-----------+
33 rows in set (0.00 sec)

(第二種清空數據保留表結構的方式)
MariaDB [hellodb]> delete from n1;
Query OK, 33 rows affected (0.00 sec)

MariaDB [hellodb]> select * from n1;
Empty set (0.00 sec)

MariaDB [hellodb]> desc n1;  （表結構還在）
+-----------+---------------------+------+-----+---------+-------+
| Field     | Type                | Null | Key | Default | Extra |
+-----------+---------------------+------+-----+---------+-------+
| stuid     | int(11)             | NO   | PRI | NULL    |       |
| Name      | varchar(50)         | NO   |     | NULL    |       |
| phone     | int(11)             | YES  |     | NULL    |       |
| Age       | tinyint(3) unsigned | NO   |     | NULL    |       |
| Gender    | enum('F','M')       | NO   |     | NULL    |       |
| ClassID   | tinyint(3) unsigned | YES  |     | NULL    |       |
| TeacherID | int(10) unsigned    | YES  |     | NULL    |       |
+-----------+---------------------+------+-----+---------+-------+
7 rows in set (0.00 sec)

DQL語句

查詢語句：SELECT （單表和多表）

單表操作
語法：

SELECT
[ALL | DISTINCT | DISTINCTROW ]
[SQL_CACHE | SQL_NO_CACHE]
select_expr [, select_expr ...]
[FROM table_references
[WHERE where_condition]
[GROUP BY {col_name | expr | position}
[ASC | DESC], ... [WITH ROLLUP]]
[HAVING where_condition]
[ORDER BY {col_name | expr | position}
[ASC | DESC], ...]
[LIMIT {[offset,] row_count | row_count OFFSET offset}]
[FOR UPDATE | LOCK IN SHARE MODE]

說明：

  • 欄位顯示可以使用別名： col1 AS alias1, col2 AS alias2, ...
  • WHERE子句：指明過濾條件以實現“選擇”的功能： 過濾條件：布爾型表達式 算術操作符：+, -, *,
    /, % 比較操作符：=,<=>（相等或都為空）, <>, !=(非標準SQL), >, >=, <, <= BETWEEN min_num
    AND max_num IN (element1, element2, ...) IS NULL IS NOT NULL SELECT DISTINCT 去除重覆
    列，範例：SELECT DISTINCT gender FROM students; LIKE: % 任意長度的任意字元 _ 任意單個字
    符 RLIKE：正則表達式，索引失效，不建議使用 REGEXP：匹配字元串可用正則表達式書寫模式，
    同上 邏輯操作符：NOT，AND，OR，XOR
  • GROUP：根據指定的條件把查詢結果進行“分組”以用於做“聚合”運算 常見聚合函數：avg(), max(),
    min(), count(), sum() HAVING: 對分組聚合運算後的結果指定過濾條件
  • ORDER BY: 根據指定的欄位對查詢結果進行排序 升序：ASC 降序：DESC
  • LIMIT [[offset,]row_count]：對查詢的結果進行輸出行數數量限制
  • 對查詢結果中的數據請求施加“鎖” FOR UPDATE: 寫鎖，獨占或排它鎖，只有一個讀和寫操作
    LOCK IN SHARE MODE: 讀鎖，共用鎖，同時多個讀操作

範例：

TRUNCATE TABLE tbl_name;
SELECT
[ALL | DISTINCT | DISTINCTROW ]
[SQL_CACHE | SQL_NO_CACHE]
select_expr [, select_expr ...]
[FROM table_references
[WHERE where_condition]
[GROUP BY {col_name | expr | position}
[ASC | DESC], ... [WITH ROLLUP]]
[HAVING where_condition]
[ORDER BY {col_name | expr | position}
[ASC | DESC], ...]
[LIMIT {[offset,] row_count | row_count OFFSET offset}]
[FOR UPDATE | LOCK IN SHARE MODE]
DESC students;
INSERT INTO students VALUES(1,'tom'，'m'),(2,'alice','f');
INSERT INTO students(id,name) VALUES(3,'jack'),(4,'allen');
SELECT * FROM students WHERE id < 3;
SELECT * FROM students WHERE gender='m';
SELECT * FROM students WHERE gender IS NULL;
SELECT * FROM students WHERE gender IS NOT NULL;
SELECT * FROM students ORDER BY name DESC LIMIT 2;
SELECT * FROM students ORDER BY name DESC LIMIT 1,2;
SELECT * FROM students WHERE id >=2 and id <=4
SELECT * FROM students WHERE BETWEEN 2 AND 4
SELECT * FROM students WHERE name LIKE ‘t%’
SELECT * FROM students WHERE name RLIKE '.*[lo].*';
SELECT id stuid,name as stuname FROM students
  1. 單表實驗：
  • 展示表裡的所有內容*代表所有欄位，也可以挑指定欄位來顯示。
MariaDB [hellodb]> select * from s1;
+-------+---------------+-------+-----+--------+---------+-----------+
| StuID | Name          | phone | Age | Gender | ClassID | TeacherID |
+-------+---------------+-------+-----+--------+---------+-----------+
|     1 | Shi Zhongyu   |  NULL |  22 | M      |       2 |         3 |
|     2 | Shi Potian    |  NULL |  22 | M      |       1 |         7 |
|     3 | Xie Yanke     |  NULL |  53 | M      |       2 |        16 |
|     4 | Ding Dian     |  NULL |  32 | M      |       4 |         4 |
|     5 | Yu Yutong     |  NULL |  26 | M      |       3 |         1 |
|     6 | Shi Qing      |  NULL |  46 | M      |       5 |      NULL |
|     7 | Xi Ren        |  NULL |  19 | F      |       3 |      NULL |
|     8 | Lin Daiyu     |  NULL |  17 | F      |       7 |      NULL |
|     9 | Ren Yingying  |  NULL |  20 | F      |       6 |      NULL |
.... 省略掉
+-------+---------------+-------+-----+--------+---------+-----------+
34 rows in set (0.00 sec)
  • 甚至可以做數字運算
MariaDB [hellodb]> select 2*3;
+-----+
| 2*3 |
+-----+
|   6 |
+-----+
1 row in set (0.01 sec)

MariaDB [hellodb]> select 2*3 from teachers;  (指定一個表，表裡有幾行做幾次數字運算和AWK很相似)
+-----+
| 2*3 |
+-----+
|   6 |
|   6 |
|   6 |
|   6 |
+-----+
4 rows in set (0.00 sec)

MariaDB [hellodb]> select * from teachers;
+-----+---------------+-----+--------+
| TID | Name          | Age | Gender |
+-----+---------------+-----+--------+
|   1 | Song Jiang    |  45 | M      |
|   2 | Zhang Sanfeng |  94 | M      |
|   3 | Miejue Shitai |  77 | F      |
|   4 | Lin Chaoying  |  93 | F      |
+-----+---------------+-----+--------+
4 rows in set (0.00 sec)
  • 指定欄位名更改 加*的話不行
MariaDB [hellodb]> select '韋小寶',name from teachers;
+-----------+---------------+
| 韋小寶    | name          |
+-----------+---------------+
| 韋小寶    | Song Jiang    |
| 韋小寶    | Zhang Sanfeng |
| 韋小寶    | Miejue Shitai |
| 韋小寶    | Lin Chaoying  |
+-----------+---------------+
4 rows in set (0.00 sec)

MariaDB [hellodb]> select '韋小寶',name,age,gender from teachers;
+-----------+---------------+-----+--------+
| 韋小寶    | name          | age | gender |
+-----------+---------------+-----+--------+
| 韋小寶    | Song Jiang    |  45 | M      |
| 韋小寶    | Zhang Sanfeng |  94 | M      |
| 韋小寶    | Miejue Shitai |  77 | F      |
| 韋小寶    | Lin Chaoying  |  93 | F      |
+-----------+---------------+-----+--------+
4 rows in set (0.00 sec)

(只是顯示效果更改)
MariaDB [hellodb]> select * from teachers;
+-----+---------------+-----+--------+
| TID | Name          | Age | Gender |
+-----+---------------+-----+--------+
|   1 | Song Jiang    |  45 | M      |
|   2 | Zhang Sanfeng |  94 | M      |
|   3 | Miejue Shitai |  77 | F      |
|   4 | Lin Chaoying  |  93 | F      |
+-----+---------------+-----+--------+
4 rows in set (0.00 sec)
  • 對錶頭起別名顯示
MariaDB [hellodb]> select '韋小寶',name as "姓名",age "年齡",gender from teachers;
+-----------+---------------+--------+--------+
| 韋小寶    | 姓名          | 年齡   | gender |
+-----------+---------------+--------+--------+
| 韋小寶    | Song Jiang    |     45 | M      |
| 韋小寶    | Zhang Sanfeng |     94 | M      |
| 韋小寶    | Miejue Shitai |     77 | F      |
| 韋小寶    | Lin Chaoying  |     93 | F      |
+-----------+---------------+--------+--------+
4 rows in set (0.01 sec)
  • 行過濾：挑出性別不是M的 !=是非標準的SQL語法 標準的為<>
MariaDB [hellodb]>  select * from s1 where gender != 'M';  (只能在MySQL資料庫使用)
+-------+---------------+-------+-----+--------+---------+-----------+
| StuID | Name          | phone | Age | Gender | ClassID | TeacherID |
+-------+---------------+-------+-----+--------+---------+-----------+
|     7 | Xi Ren        |  NULL |  19 | F      |       3 |      NULL |
|     8 | Lin Daiyu     |  NULL |  17 | F      |       7 |      NULL |
|     9 | Ren Yingying  |  NULL |  20 | F      |       6 |      NULL |
|    10 | Yue Lingshan  |  NULL |  19 | F      |       3 |      NULL |
|    12 | Wen Qingqing  |  NULL |  19 | F      |       1 |      NULL |
|    14 | Lu Wushuang   |  NULL |  17 | F      |       3 |      NULL |
|    19 | Xue Baochai   |  NULL |  18 | F      |       6 |      NULL |
|    20 | Diao Chan     |  NULL |  19 | F      |       7 |      NULL |
|    21 | Huang Yueying |  NULL |  22 | F      |       6 |      NULL |
|    22 | Xiao Qiao     |  NULL |  20 | F      |       1 |      NULL |
|    27 | liudehua      |  NULL |  18 | F      |       1 |      NULL |
|    30 | wuzetian      |  NULL |  21 | F      |    NULL |      NULL |
|    33 | Miejue Shitai |  NULL |  18 | F      |      77 |      NULL |
|    34 | Lin Chaoying  |  NULL |  18 | F      |      93 |      NULL |
+-------+-------------
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