MYSQL命令（二）

时间:2019-11-30
本文章向大家介绍MYSQL命令（二），主要包括MYSQL命令（二）使用实例、应用技巧、基本知识点总结和需要注意事项，具有一定的参考价值，需要的朋友可以参考一下。

查看表结构和alter 增加、修改、删除字段

16.查看表结构

(1)desc 表名; 

mysql> desc runoob_tbl;
+-----------------+------------------+------+-----+---------+----------------+
| Field           | Type             | Null | Key | Default | Extra          |
+-----------------+------------------+------+-----+---------+----------------+
| runoob_id       | int(10) unsigned | NO   | PRI | NULL    | auto_increment |
| runoob_title    | varchar(100)     | NO   |     | NULL    |                |
| runoob_author   | varchar(40)      | NO   |     | NULL    |                |
| submission_date | date             | YES  |     | NULL    |                |
+-----------------+------------------+------+-----+---------+----------------+
4 rows in set (0.00 sec)

(2)describe表名;

mysql> describe runoob_tbl;
+-----------------+------------------+------+-----+---------+----------------+
| Field           | Type             | Null | Key | Default | Extra          |
+-----------------+------------------+------+-----+---------+----------------+
| runoob_id       | int(10) unsigned | NO   | PRI | NULL    | auto_increment |
| runoob_title    | varchar(100)     | NO   |     | NULL    |                |
| runoob_author   | varchar(40)      | NO   |     | NULL    |                |
| submission_date | date             | YES  |     | NULL    |                |
+-----------------+------------------+------+-----+---------+----------------+
4 rows in set (0.00 sec)

（3）show columns from 表名;

mysql> show columns from runoob_tbl;
+-----------------+------------------+------+-----+---------+----------------+
| Field           | Type             | Null | Key | Default | Extra          |
+-----------------+------------------+------+-----+---------+----------------+
| runoob_id       | int(10) unsigned | NO   | PRI | NULL    | auto_increment |
| runoob_title    | varchar(100)     | NO   |     | NULL    |                |
| runoob_author   | varchar(40)      | NO   |     | NULL    |                |
| submission_date | date             | YES  |     | NULL    |                |
+-----------------+------------------+------+-----+---------+----------------+
4 rows in set (0.00 sec)

 (4) show create table 表名;

mysql> show create table  runoob_tbl;
+------------+----------------------------------------------------------------------------------------+
| Table      | Create Table                                                                           |
+------------+----------------------------------------------------------------------------------------+
| runoob_tbl | CREATE TABLE `runoob_tbl` (
  `runoob_id` int(10) unsigned NOT NULL AUTO_INCREMENT,
  `runoob_title` varchar(100) NOT NULL,
  `runoob_author` varchar(40) NOT NULL,
  `submission_date` date DEFAULT NULL,
  PRIMARY KEY (`runoob_id`)
) ENGINE=InnoDB AUTO_INCREMENT=4 DEFAULT CHARSET=utf8                                                |
+------------+----------------------------------------------------------------------------------------

(5) show fields from 表名;

mysql> show fields from runoob_tbl;
+-----------------+------------------+------+-----+---------+----------------+
| Field           | Type             | Null | Key | Default | Extra          |
+-----------------+------------------+------+-----+---------+----------------+
| runoob_id       | int(10) unsigned | NO   | PRI | NULL    | auto_increment |
| runoob_title    | varchar(100)     | NO   |     | NULL    |                |
| runoob_author   | varchar(40)      | NO   |     | NULL    |                |
| submission_date | date             | YES  |     | NULL    |                |
+-----------------+------------------+------+-----+---------+----------------+
4 rows in set (0.00 sec)

17.alter命令

(1) 添加字段：alter table 表名 add 字段 类型;

mysql> alter table runoob_tbl add runoob_extra varchar(40);
Query OK, 0 rows affected (0.16 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> show columns from runoob_tbl;
+-----------------+------------------+------+-----+---------+----------------+
| Field           | Type             | Null | Key | Default | Extra          |
+-----------------+------------------+------+-----+---------+----------------+
| runoob_id       | int(10) unsigned | NO   | PRI | NULL    | auto_increment |
| runoob_title    | varchar(100)     | NO   |     | NULL    |                |
| runoob_author   | varchar(40)      | NO   |     | NULL    |                |
| submission_date | date             | YES  |     | NULL    |                |
| runoob_extra    | varchar(40)      | YES  |     | NULL    |                |
+-----------------+------------------+------+-----+---------+----------------+
5 rows in set (0.00 sec)

 (2) 删除字段：alter table表名 drop 字段;

mysql> alter table runoob_tbl drop runoob_extra;
Query OK, 0 rows affected (0.08 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> show full fields from runoob_tbl;
+-----------------+------------------+-----------------+------+-----+---------+----------------+---------------------------------+---------+
| Field           | Type             | Collation       | Null | Key | Default | Extra          | Privileges                      | Comment |
+-----------------+------------------+-----------------+------+-----+---------+----------------+---------------------------------+---------+
| runoob_id       | int(10) unsigned | NULL            | NO   | PRI | NULL    | auto_increment | select,insert,update,references |         |
| runoob_title    | varchar(100)     | utf8_general_ci | NO   |     | NULL    |                | select,insert,update,references |         |
| runoob_author   | varchar(40)      | utf8_general_ci | NO   |     | NULL    |                | select,insert,update,references |         |
| submission_date | date             | NULL            | YES  |     | NULL    |                | select,insert,update,references |         |
+-----------------+------------------+-----------------+------+-----+---------+----------------+---------------------------------+---------+
4 rows in set (0.00 sec)

 (3) 修改字段：alter table表名 modify  字段 类型;

mysql> alter table runoob_tbl modify runoob_title varchar(128);
Query OK, 0 rows affected (0.08 sec)
Records: 0  Duplicates: 0  Warnings: 0
mysql> desc runoob_tbl runoob_title;
+--------------+--------------+------+-----+---------+-------+
| Field        | Type         | Null | Key | Default | Extra |
+--------------+--------------+------+-----+---------+-------+
| runoob_title | varchar(128) | YES  |     | NULL    |       |
+--------------+--------------+------+-----+---------+-------+
1 row in set (0.00 sec)

 18.插入数据语法：INSERT INTO table_name ( field1, field2,...fieldN ) VALUES( value1, value2,...valueN );

mysql> INSERT INTO runoob_tbl (runoob_title, runoob_author, submission_date) VALUES ("学习PHP", " runoob.com", NOW());
Query OK, 1 row affected, 1 warning (0.00 sec)
mysql> INSERT INTO runoob_tbl (runoob_title, runoob_author, submission_date) VALUES ("JAVA 教程", "RUNOOB.COM", '2016-05-06');
Query OK, 1 row affected (0.01 sec)

19.查询数据语法：SELECT column_name,column_nameFROM table_name [WHERE Clause] [LIMIT N][ OFFSET M]

mysql> select * from runoob_tbl;
+-----------+--------------+---------------+-----------------+
| runoob_id | runoob_title | runoob_author | submission_date |
+-----------+--------------+---------------+-----------------+
|         1 | 学习PHP       |  runoob.com   | 2019-11-12      |
|         2 | 学习 MySQL    |  runoob.com   | 2019-11-12      |
|         3 | JAVA 教程     | RUNOOB.COM    | 2016-05-06      |
+-----------+--------------+---------------+-----------------+
3 rows in set (0.04 sec)

20.UPDATE 更新

mysql> UPDATE runoob_tbl SET runoob_title='学习 C++' WHERE runoob_id=3;
Query OK, 1 row affected (0.01 sec)
Rows matched: 1  Changed: 1  Warnings: 0
mysql> select * from runoob_tbl where runoob_id=3;
+-----------+--------------+---------------+-----------------+
| runoob_id | runoob_title | runoob_author | submission_date |
+-----------+--------------+---------------+-----------------+
|         3 | 学习 C++      | RUNOOB.COM    | 2016-05-06      |
+-----------+--------------+---------------+-----------------+
1 row in set (0.00 sec)

21.DELETE语法:DELETE FROM table_name [WHERE Clause]

mysql> DELETE FROM runoob_tbl WHERE runoob_id=3;
Query OK, 1 row affected (0.01 sec)
22.Where子句
mysql> SELECT * from runoob_tbl WHERE runoob_author=' runoob.com';
+-----------+--------------+---------------+-----------------+
| runoob_id | runoob_title | runoob_author | submission_date |
+-----------+--------------+---------------+-----------------+
|         1 | 学习PHP       |  runoob.com   | 2019-11-12      |
|         2 | 学习 MySQL    |  runoob.com   | 2019-11-12      |
+-----------+--------------+---------------+-----------------+
2 rows in set (0.00 sec)

22.LIKE子句语法：SELECT field1, field2,...fieldN FROM table_name WHERE field1 LIKE condition1 [AND [OR]] filed2 = 'somevalue'

mysql>  SELECT * from runoob_tbl  WHERE runoob_author LIKE '%COM';
+-----------+--------------+---------------+-----------------+
| runoob_id | runoob_title | runoob_author | submission_date |
+-----------+--------------+---------------+-----------------+
|         1 | 学习PHP      | runoob.com    | 2019-11-12       |
|         2 | 学习 MySQL   | runoob.com    | 2019-11-12       |
+-----------+--------------+---------------+-----------------+
2 rows in set (0.00 sec)

 23.分组GROUP BY 语法：SELECT column_name, function(column_name) FROM table_name WHERE column_name operator value GROUP BY column_name;

mysql> select count(*), runoob_author  from runoob_tbl group by runoob_author;
+----------+---------------+
| count(*) | runoob_author |
+----------+---------------+
|        2 | runoob        |
|        2 | runoob.com    |
+----------+---------------+
2 rows in set (0.00 sec)

补充：with rollup可以实现在分组统计数据基础上再进行相同的统计（SUM,AVG,COUNT…）。

mysql> select sum(runoob_id), runoob_author  from runoob_tbl group by runoob_author with rollup;
+----------------+---------------+
| sum(runoob_id) | runoob_author |
+----------------+---------------+
|             29 | runoob        |
|              3 | runoob.com    |
|             32 | NULL          |
+----------------+---------------+
3 rows in set (0.00 sec)

mysql> select avg(runoob_id), runoob_author  from runoob_tbl group by runoob_author with rollup;
+----------------+---------------+
| avg(runoob_id) | runoob_author |
+----------------+---------------+
|        14.5000 | runoob        |
|         1.5000 | runoob.com    |
|         8.0000 | NULL          |
+----------------+---------------+
3 rows in set (0.00 sec)

mysql> select count(runoob_id), runoob_author  from runoob_tbl group by runoob_author with rollup;
+------------------+---------------+
| count(runoob_id) | runoob_author |
+------------------+---------------+
|                2 | runoob        |
|                2 | runoob.com    |
|                4 | NULL          |
+------------------+---------------+
3 rows in set (0.00 sec)　

 24.ORDER BY子句查询数据语法：SELECT field1, field2,...fieldN FROM table_name1, table_name2...ORDER BY field1 [ASC [DESC][默认 ASC]], [field2...] [ASC [DESC][默认 ASC]]

mysql> select * from runoob_tbl order by runoob_id desc;
+-----------+--------------+---------------+-----------------+
| runoob_id | runoob_title | runoob_author | submission_date |
+-----------+--------------+---------------+-----------------+
|        18 | 学习JAVA     | runoob        | 2019-11-28      |
|        11 | 学习JAVA     | runoob        | 2019-11-18      |
|         2 | 学习 MySQL   | runoob.com    | 2019-11-12      |
|         1 | 学习PHP      | runoob.com    | 2019-11-12      |
+-----------+--------------+---------------+-----------------+
4 rows in set (0.00 sec)

25.NULL值处理：

mysql> select * from runoob_tbl where runoob_title is not null;
+-----------+--------------+---------------+-----------------+
| runoob_id | runoob_title | runoob_author | submission_date |
+-----------+--------------+---------------+-----------------+
|         1 | 学习PHP      | runoob.com    | 2019-11-12      |
|         2 | 学习 MySQL   | runoob.com    | 2019-11-12      |
|        11 | 学习JAVA     | runoob        | 2019-11-18      |
|        18 | 学习JAVA     | runoob        | 2019-11-28      |
+-----------+--------------+---------------+-----------------+
4 rows in set (0.00 sec)

查询null值：

mysql> insert runoob_tbl values(5,null,'RUNOOB','2019-11-29');
Query OK, 1 row affected (0.01 sec)

mysql> select * from runoob_tbl where runoob_title is null;
+-----------+--------------+---------------+-----------------+
| runoob_id | runoob_title | runoob_author | submission_date |
+-----------+--------------+---------------+-----------------+
|         5 | NULL         | RUNOOB        | 2019-11-29      |
+-----------+--------------+---------------+-----------------+
1 row in set (0.01 sec)

26.正则表达式：

mysql> select * from runoob_tbl where runoob_author REGEXP '^runoob.';
+-----------+--------------+---------------+-----------------+
| runoob_id | runoob_title | runoob_author | submission_date |
+-----------+--------------+---------------+-----------------+
|         1 | 学习PHP      | runoob.com    | 2019-11-12      |
|         2 | 学习 MySQL   | runoob.com    | 2019-11-12      |
+-----------+--------------+---------------+-----------------+
2 rows in set (0.00 sec)

mysql> 
mysql> select * from runoob_tbl where runoob_author REGEXP '^RUN';
+-----------+--------------+---------------+-----------------+
| runoob_id | runoob_title | runoob_author | submission_date |
+-----------+--------------+---------------+-----------------+
|         1 | 学习PHP      | runoob.com    | 2019-11-12      |
|         2 | 学习 MySQL   | runoob.com    | 2019-11-12      |
|         5 | NULL         | RUNOOB        | 2019-11-29      |
|        11 | 学习JAVA     | runoob        | 2019-11-18      |
|        18 | 学习JAVA     | runoob        | 2019-11-28      |
+-----------+--------------+---------------+-----------------+
5 rows in set (0.00 sec)

　　

　

　

原文地址：https://www.cnblogs.com/loytime/p/11953325.html

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