学习数据库MySQL
2024-04-12 08:08:30
查询本机数据库: show databases;
mysql> show databases;
+--------------------+
| Database |
+--------------------+
| information_schema |
| mysql |
| performance_schema |
| sys |
| test |
+--------------------+
5 rows in set (0.01 sec)创建数据库: create database ‘数据库名字’;
create database test;
Query OK, 1 row affected (0.01 sec)查询数据库下的表：show tables;
mysql> show tables;
+----------------+
| Tables_in_test |
+----------------+
| article |
| article2 |
| cagety |
| user |
| wechat |
| wechat_list |
+----------------+
6 rows in set (0.00 sec)
选择数据库: use test;
mysql> use test;
Database changed向数据表插入数据: insert into article (‘键值’, ‘键值’, ‘键值’) values (‘内容’, ‘内容’, ‘内容’)
mysql> # 插入数据
mysql>
mysql> insert into article (title, author, date)-> values-> ('我想吃肉', 'bob', now());
Query OK, 1 row affected, 1 warning (0.01 sec)查询数据表下的结构：show columns from ‘数据表名称’;
mysql> show columns from article;
+--------+-------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+--------+-------------+------+-----+---------+----------------+
| id | int(11) | NO | PRI | NULL | auto_increment |
| title | varchar(50) | YES | | NULL | |
| author | varchar(50) | YES | | NULL | |
| date | date | YES | | NULL | |
+--------+-------------+------+-----+---------+----------------+
4 rows in set (0.00 sec)mysql>查询数据表下的所有内容：select * from ‘数据库表’;
mysql> select * from article;
+----+-----------------------------------+---------------+------------+
| id | title | author | date |
+----+-----------------------------------+---------------+------------+
| 1 | 今晚聚餐哦! | bob | 2018-05-01 |
| 2 | 我想吃肉 | bob | 2018-05-01 |
| 4 | 好呀，今晚买多点牛肉丸 | shaw | 2018-05-01 |
| 6 | 一波万波 | yibowanbo.com | 2018-04-30 |
| 8 | 一波 | bo | 2018-05-01 |
| 9 | 万波 | wanbo | 2018-05-01 |
+----+-----------------------------------+---------------+------------+
6 rows in set (0.00 sec)mysql>根据条件查询数据表下的内容：
select * from ‘数据库表’ where ‘键值’ = ‘条件’;
select ‘键值’ from ‘数据库表’;
mysql> select * from article where id = 2;
+----+--------------+--------+------------+
| id | title | author | date |
+----+--------------+--------+------------+
| 2 | 我想吃肉 | bob | 2018-05-01 |
+----+--------------+--------+------------+
1 row in set (0.00 sec)mysql># 也是可以使用like，like等于=号mysql> select * from article where id like 2;
+----+--------------+--------+------------+
| id | title | author | date |
+----+--------------+--------+------------+
| 2 | 我想吃肉 | bob | 2018-05-01 |
+----+--------------+--------+------------+
1 row in set (0.00 sec)mysql>mysql> select author from article;
+---------------+
| author |
+---------------+
| bob |
| bob |
| shaw |
| yibowanbo.com |
| bo |
| wanbo |
+---------------+
6 rows in set (0.00 sec)mysql>修改数据表数据：update ‘数据库表’ set ‘要修改的字段键值’ = ‘修改的内容’ where 条件
update article set title='今晚聚餐哦!' where id = 1;mysql> update article set title='今晚聚餐哦!' where id = 1;
Query OK, 1 row affected (0.01 sec)
Rows matched: 1 Changed: 1 Warnings: 0
删除数据表里面的数据：delete from ‘数据表’ where 条件;
delete from article where id = 3;mysql> # 删除数据表里面的数据
mysql>
mysql> delete from article where id = 3;
Query OK, 1 row affected (0.00 sec)union用法：select ‘键’ from ‘数据库表1’ union select ‘键’ from ‘数据库表2’;
链接查询多表之间相同的键值，返回不重复键值
MySQL UNION 操作符用于连接两个以上的 SELECT 语句的结果组合到一个结果集合中。多个 SELECT 语句会删除重复的数据。
mysql> select * from user;
+----+-----------+
| id | username |
+----+-----------+
| 1 | 林大和 |
| 4 | 梁凤波 |
+----+-----------+
2 rows in set (0.00 sec)mysql> select * from wechat_list;
+----+-----------+
| id | username |
+----+-----------+
| 1 | 量风波 |
| 2 | 梁凤波 |
+----+-----------+
2 rows in set (0.00 sec)mysql> select username from user union select username from wechat_list;
+-----------+
| username |
+-----------+
| 林大和 |
| 梁凤波 |
| 量风波 |
+-----------+
3 rows in set (0.00 sec)mysql>降升排序：select * from ‘数据库表’ order by 键值 ASC;
select * from '数据库表' order by 键值 ASC;ASC升序DESC 降序mysql>
mysql>
mysql> select * from article order by title ASC;
+----+-----------------------------------+---------------+------------+
| id | title | author | date |
+----+-----------------------------------+---------------+------------+
| 6 | 一波万波 | yibowanbo.com | 2018-04-30 |
| 1 | 今晚聚餐哦! | bob | 2018-05-01 |
| 4 | 好呀，今晚买多点牛肉丸 | shaw | 2018-05-01 |
| 2 | 我想吃肉 | bob | 2018-05-01 |
+----+-----------------------------------+---------------+------------+
4 rows in set (0.00 sec)mysql>
mysql> select * from article order by title DESC;
+----+-----------------------------------+---------------+------------+
| id | title | author | date |
+----+-----------------------------------+---------------+------------+
| 2 | 我想吃肉 | bob | 2018-05-01 |
| 4 | 好呀，今晚买多点牛肉丸 | shaw | 2018-05-01 |
| 1 | 今晚聚餐哦! | bob | 2018-05-01 |
| 6 | 一波万波 | yibowanbo.com | 2018-04-30 |
+----+-----------------------------------+---------------+------------+
4 rows in set (0.00 sec)统计分组：select date, count(*) from article group by date;
mysql> select * from article;
+----+-----------------------------------+---------------+------------+
| id | title | author | date |
+----+-----------------------------------+---------------+------------+
| 1 | 今晚聚餐哦! | bob | 2018-05-01 |
| 2 | 我想吃肉 | bob | 2018-05-01 |
| 4 | 好呀，今晚买多点牛肉丸 | shaw | 2018-05-01 |
| 6 | 一波万波 | yibowanbo.com | 2018-04-30 |
+----+-----------------------------------+---------------+------------+
4 rows in set (0.00 sec)mysql>
mysql> select date, count(*) from article group by date;
+------------+----------+
| date | count(*) |
+------------+----------+
| 2018-04-30 | 1 |
| 2018-05-01 | 3 |
+------------+----------+
2 rows in set (0.00 sec)NULL运用
# 直接等是查询不出来的，需要用is null或is not nullmysql> select * from cagety where count like NULL;
Empty set (0.00 sec)mysql>
mysql> select * from cagety where count is NULL;
+--------+-------+
| author | count |
+--------+-------+
| go | NULL |
| css | NULL |
+--------+-------+
2 rows in set (0.00 sec)mysql>
mysql> select * from cagety where count is not null;
+--------+-------+
| author | count |
+--------+-------+
| go | 20 |
| html | 20 |
| nodejs | 10 |
| php | 30 |
+--------+-------+
4 rows in set (0.00 sec)mysql>mysql 正则使用
mysql> SELECT name FROM person_tbl WHERE name REGEXP '^st';
查找name字段中以'ok'为结尾的所有数据：mysql> SELECT name FROM person_tbl WHERE name REGEXP 'ok$';
查找name字段中包含'mar'字符串的所有数据：mysql> SELECT name FROM person_tbl WHERE name REGEXP 'mar';
查找name字段中以元音字符开头或以'ok'字符串结尾的所有数据：mysql> SELECT name FROM person_tbl WHERE name REGEXP '^[aeiou]|ok$';mysql> select * from article
-> ;
+----+-----------------------------------+---------------+------------+
| id | title | author | date |
+----+-----------------------------------+---------------+------------+
| 1 | 今晚聚餐哦! | bob | 2018-05-01 |
| 2 | 我想吃肉 | bob | 2018-05-01 |
| 4 | 好呀，今晚买多点牛肉丸 | shaw | 2018-05-01 |
| 6 | 一波万波 | yibowanbo.com | 2018-04-30 |
| 8 | 一波 | bo | 2018-05-01 |
| 9 | 万波 | wanbo | 2018-05-01 |
+----+-----------------------------------+---------------+------------+
6 rows in set (0.00 sec)mysql>
mysql> select title from article where title REGEXP '^波';
Empty set (0.00 sec)mysql>
mysql>
mysql> select title from article where title REGEXP '^一';
+--------------+
| title |
+--------------+
| 一波万波 |
| 一波 |
+--------------+
2 rows in set (0.00 sec)mysql>
mysql> select title from article where title REGEXP '波$';
+--------------+
| title |
+--------------+
| 一波万波 |
| 一波 |
| 万波 |
+--------------+
3 rows in set (0.00 sec)
mysql>
mysql>
mysql>
mysql> select author from article where author regexp 'o';
+---------------+
| author |
+---------------+
| bob |
| bob |
| yibowanbo.com |
| bo |
| wanbo |
+---------------+
5 rows in set (0.00 sec)增加字段
mysql> # 增加字段
mysql>
mysql> alter table article add content varchar(200);
Query OK, 0 rows affected (0.07 sec)
Records: 0 Duplicates: 0 Warnings: 0mysql>
mysql> show columns from article;
+---------+--------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+---------+--------------+------+-----+---------+----------------+
| id | int(11) | NO | PRI | NULL | auto_increment |
| title | varchar(100) | NO | | NULL | |
| author | varchar(40) | NO | | NULL | |
| date | date | YES | | NULL | |
| content | varchar(200) | YES | | NULL | |
+---------+--------------+------+-----+---------+----------------+
5 rows in set (0.00 sec)mysql> # 删除字段删除字段
mysql>
mysql> alter table article drop content;
Query OK, 0 rows affected (0.06 sec)
Records: 0 Duplicates: 0 Warnings: 0mysql>
mysql> show columns from article;
+--------+--------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+--------+--------------+------+-----+---------+----------------+
| id | int(11) | NO | PRI | NULL | auto_increment |
| title | varchar(100) | NO | | NULL | |
| author | varchar(40) | NO | | NULL | |
| date | date | YES | | NULL | |
+--------+--------------+------+-----+---------+----------------+
4 rows in set (0.00 sec)mysql> select * from article;
+----+-----------------------------------+---------------+------------+
| id | names | author | date |
+----+-----------------------------------+---------------+------------+
| 1 | 今晚聚餐哦! | bob | 2018-05-01 |
| 2 | 我想吃肉 | bob | 2018-05-01 |
| 4 | 好呀，今晚买多点牛肉丸 | shaw | 2018-05-01 |
| 6 | 一波万波 | yibowanbo.com | 2018-04-30 |
| 8 | 一波 | bo | 2018-05-01 |
| 9 | 万波 | wanbo | 2018-05-01 |
+----+-----------------------------------+---------------+------------+
6 rows in set (0.00 sec)修改字段的类型和键值
mysql>
mysql> alter table article change names title varchar(50);
Query OK, 0 rows affected (0.03 sec)
Records: 0 Duplicates: 0 Warnings: 0mysql> select * from article;
+----+-----------------------------------+---------------+------------+
| id | title | author | date |
+----+-----------------------------------+---------------+------------+
| 1 | 今晚聚餐哦! | bob | 2018-05-01 |
| 2 | 我想吃肉 | bob | 2018-05-01 |
| 4 | 好呀，今晚买多点牛肉丸 | shaw | 2018-05-01 |
| 6 | 一波万波 | yibowanbo.com | 2018-04-30 |
| 8 | 一波 | bo | 2018-05-01 |
| 9 | 万波 | wanbo | 2018-05-01 |
+----+-----------------------------------+---------------+------------+
6 rows in set (0.00 sec)修改字段的类型
mysql>
mysql> alter table article modify author varchar(50);
Query OK, 0 rows affected (0.07 sec)
Records: 0 Duplicates: 0 Warnings: 0mysql>
mysql> show columns from article;
+--------+-------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+--------+-------------+------+-----+---------+----------------+
| id | int(11) | NO | PRI | NULL | auto_increment |
| title | varchar(50) | YES | | NULL | |
| author | varchar(50) | YES | | NULL | |
| date | date | YES | | NULL | |
+--------+-------------+------+-----+---------+----------------+
4 rows in set (0.00 sec)
修改设置默认值
mysql>
mysql> alter table article alter date set default '2018-05-03';
Query OK, 0 rows affected (0.03 sec)
Records: 0 Duplicates: 0 Warnings: 0mysql> show columns from article;
+--------+-------------+------+-----+------------+----------------+
| Field | Type | Null | Key | Default | Extra |
+--------+-------------+------+-----+------------+----------------+
| id | int(11) | NO | PRI | NULL | auto_increment |
| title | varchar(50) | YES | | NULL | |
| author | varchar(50) | YES | | NULL | |
| date | date | YES | | 2018-05-03 | |
+--------+-------------+------+-----+------------+----------------+
4 rows in set (0.00 sec)mysql>删除默认值
mysql> alter table article alter date drop default;
Query OK, 0 rows affected (0.03 sec)
Records: 0 Duplicates: 0 Warnings: 0mysql> show columns from article;
+--------+-------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+--------+-------------+------+-----+---------+----------------+
| id | int(11) | NO | PRI | NULL | auto_increment |
| title | varchar(50) | YES | | NULL | |
| author | varchar(50) | YES | | NULL | |
| date | date | YES | | NULL | |
+--------+-------------+------+-----+---------+----------------+
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