一：显示数据库及模糊查询（like）
mysql> show databases;
+--------------------+
| Database |
+--------------------+
| db_classes |
| db_user |
| information_schema |
| mysql |
| performance_schema |
| sys |
+--------------------+
6 rows in set (0.00 sec)mysql> show databases like "db%";
+----------------+
| Database (db%) |
+----------------+
| db_classes |
| db_user |
+----------------+
2 rows in set (0.01 sec)mysql> use db_user;
Database changed
mysql> show tables;
+-------------------+
| Tables_in_db_user |
+-------------------+
| db_info |
+-------------------+
1 row in set (0.00 sec)mysql> select * from db_info;
+----+------+--------+------+---------+
| id | name | gender | age | address |
+----+------+--------+------+---------+
| 1 | zs | 男 | 18 | 西安 |
| 2 | zs1 | 女 | 18 | NULL |
| 3 | zs2 | 女 | 18 | NULL |
+----+------+--------+------+---------+
3 rows in set (0.00 sec)
mysql> desc db_info;
+---------+--------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+---------+--------------+------+-----+---------+-------+
| id | int | NO | PRI | NULL | |
| name | varchar(255) | NO | | NULL | |
| gender | char(1) | YES | | NULL | |
| age | int | YES | | 18 | |
| address | varchar(255) | YES | | NULL | |
+---------+--------------+------+-----+---------+-------+
5 rows in set (0.00 sec)mysql> use db_classes;
Database changed
mysql> show tables;
+----------------------+
| Tables_in_db_classes |
+----------------------+
| db_hero |
+----------------------+
1 row in set (0.00 sec)mysql> select *from db_hero;
+------+--------------+--------------+------+--------+-----------+--------------+--------------+--------+
| id | name | nickname | age | gender | address | wuqi | world | types |
+------+--------------+--------------+------+--------+-----------+--------------+--------------+--------+
| 1 | 孙悟空 | 齐天大圣 | 500 | 男 | 花果山 | 金箍棒 | 西游世界 | 妖族 |
| 2 | 猪刚鬣 | 猪八戒 | 600 | 男 | 高老庄 | 九齿钉耙 | 西游世界 | 妖族 |
| 3 | 武松 | 打虎哥 | 30 | 男 | 吴国 | 拳头 | 水浒世界 | 人族 |
| 4 | 鲁智深 | 杨柳哥 | 20 | 男 | 吴国 | 铲杖 | 水浒世界 | 人族 |
| 5 | 太白金星 | 太上老君 | 5000 | 男 | 天庭 | 毛笔 | 西游世界 | 仙族 |
+------+--------------+--------------+------+--------+-----------+--------------+--------------+--------+
5 rows in set (0.01 sec)mysql> desc db_hero;
+----------+--------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+----------+--------------+------+-----+---------+-------+
| id | int | YES | | NULL | |
| name | varchar(100) | YES | | NULL | |
| nickname | varchar(100) | YES | | NULL | |
| age | int | YES | | NULL | |
| gender | varchar(20) | YES | | NULL | |
| address | varchar(100) | YES | | NULL | |
| wuqi | varchar(100) | YES | | NULL | |
| world | varchar(100) | YES | | NULL | |
| types | varchar(20) | YES | | NULL | |
+----------+--------------+------+-----+---------+-------+
9 rows in set (0.00 sec)二：插入数据到数据库表中
mysql> insert into db_hero values(null,"武大郎","大朗",25,"男","吴国","无","水浒世界","人族");
Query OK, 1 row affected (0.00 sec)mysql> select * from db_hero;
+------+--------------+--------------+------+--------+-----------+--------------+--------------+--------+
| id | name | nickname | age | gender | address | wuqi | world | types |
+------+--------------+--------------+------+--------+-----------+--------------+--------------+--------+
| 1 | 孙悟空 | 齐天大圣 | 500 | 男 | 花果山 | 金箍棒 | 西游世界 | 妖族 |
| 2 | 猪刚鬣 | 猪八戒 | 600 | 男 | 高老庄 | 九齿钉耙 | 西游世界 | 妖族 |
| 3 | 武松 | 打虎哥 | 30 | 男 | 吴国 | 拳头 | 水浒世界 | 人族 |
| 4 | 鲁智深 | 杨柳哥 | 20 | 男 | 吴国 | 铲杖 | 水浒世界 | 人族 |
| 5 | 太白金星 | 太上老君 | 5000 | 男 | 天庭 | 毛笔 | 西游世界 | 仙族 |
| NULL | 武大郎 | 大朗 | 25 | 男 | 吴国 | 无 | 水浒世界 | 人族 |
+------+--------------+--------------+------+--------+-----------+--------------+--------------+--------+
6 rows in set (0.00 sec)mysql> insert into db_hero values(7,"武大郎","大朗",25,"男","吴国","无","水浒世界","人族");
Query OK, 1 row affected (0.01 sec)mysql> select * from db_hero;
+------+--------------+--------------+------+--------+-----------+--------------+--------------+--------+
| id | name | nickname | age | gender | address | wuqi | world | types |
+------+--------------+--------------+------+--------+-----------+--------------+--------------+--------+
| 1 | 孙悟空 | 齐天大圣 | 500 | 男 | 花果山 | 金箍棒 | 西游世界 | 妖族 |
| 2 | 猪刚鬣 | 猪八戒 | 600 | 男 | 高老庄 | 九齿钉耙 | 西游世界 | 妖族 |
| 3 | 武松 | 打虎哥 | 30 | 男 | 吴国 | 拳头 | 水浒世界 | 人族 |
| 4 | 鲁智深 | 杨柳哥 | 20 | 男 | 吴国 | 铲杖 | 水浒世界 | 人族 |
| 5 | 太白金星 | 太上老君 | 5000 | 男 | 天庭 | 毛笔 | 西游世界 | 仙族 |
| NULL | 武大郎 | 大朗 | 25 | 男 | 吴国 | 无 | 水浒世界 | 人族 |
| 7 | 武大郎 | 大朗 | 25 | 男 | 吴国 | 无 | 水浒世界 | 人族 |
+------+--------------+--------------+------+--------+-----------+--------------+--------------+--------+
7 rows in set (0.00 sec)三：删除数据库表中的数据
mysql> delete from db_hero where id=1;
Query OK, 1 row affected (0.01 sec)mysql> select * from db_hero;
+------+--------------+--------------+------+--------+-----------+--------------+--------------+--------+
| id | name | nickname | age | gender | address | wuqi | world | types |
+------+--------------+--------------+------+--------+-----------+--------------+--------------+--------+
| 2 | 猪刚鬣 | 猪八戒 | 600 | 男 | 高老庄 | 九齿钉耙 | 西游世界 | 妖族 |
| 3 | 武松 | 打虎哥 | 30 | 男 | 吴国 | 拳头 | 水浒世界 | 人族 |
| 4 | 鲁智深 | 杨柳哥 | 20 | 男 | 吴国 | 铲杖 | 水浒世界 | 人族 |
| 5 | 太白金星 | 太上老君 | 5000 | 男 | 天庭 | 毛笔 | 西游世界 | 仙族 |
| NULL | 武大郎 | 大朗 | 25 | 男 | 吴国 | 无 | 水浒世界 | 人族 |
| 7 | 武大郎 | 大朗 | 25 | 男 | 吴国 | 无 | 水浒世界 | 人族 |
| 8 | 红孩儿 | 无 | 25 | 男 | 妖界 | 无 | 西游世界 | 仙族 |
| NULL | 金角大王 | NULL | NULL | NULL | NULL | NULL | NULL | NULL |
| NULL | 银角大王 | NULL | NULL | 男 | NULL | NULL | NULL | NULL |
| NULL | 银角大王 | NULL | NULL | 男 | NULL | NULL | NULL | NULL |
| NULL | 孙尚香 | NULL | NULL | 女 | NULL | NULL | NULL | NULL |
| NULL | 马超 | NULL | NULL | 男 | NULL | NULL | NULL | NULL |
+------+--------------+--------------+------+--------+-----------+--------------+--------------+--------+
12 rows in set (0.00 sec)mysql> delete from db_hero where name="银角大王";
Query OK, 2 rows affected (0.00 sec)mysql> select * from db_hero;
+------+--------------+--------------+------+--------+-----------+--------------+--------------+--------+
| id | name | nickname | age | gender | address | wuqi | world | types |
+------+--------------+--------------+------+--------+-----------+--------------+--------------+--------+
| 2 | 猪刚鬣 | 猪八戒 | 600 | 男 | 高老庄 | 九齿钉耙 | 西游世界 | 妖族 |
| 3 | 武松 | 打虎哥 | 30 | 男 | 吴国 | 拳头 | 水浒世界 | 人族 |
| 4 | 鲁智深 | 杨柳哥 | 20 | 男 | 吴国 | 铲杖 | 水浒世界 | 人族 |
| 5 | 太白金星 | 太上老君 | 5000 | 男 | 天庭 | 毛笔 | 西游世界 | 仙族 |
| NULL | 武大郎 | 大朗 | 25 | 男 | 吴国 | 无 | 水浒世界 | 人族 |
| 7 | 武大郎 | 大朗 | 25 | 男 | 吴国 | 无 | 水浒世界 | 人族 |
| 8 | 红孩儿 | 无 | 25 | 男 | 妖界 | 无 | 西游世界 | 仙族 |
| NULL | 金角大王 | NULL | NULL | NULL | NULL | NULL | NULL | NULL |
| NULL | 孙尚香 | NULL | NULL | 女 | NULL | NULL | NULL | NULL |
| NULL | 马超 | NULL | NULL | 男 | NULL | NULL | NULL | NULL |
+------+--------------+--------------+------+--------+-----------+--------------+--------------+--------+
10 rows in set (0.00 sec)mysql> use db_user;
Database changed
mysql> show tables;
+-------------------+
| Tables_in_db_user |
+-------------------+
| db_info |
+-------------------+
1 row in set (0.00 sec)mysql> select *from db_info;
+----+------+--------+------+---------+
| id | name | gender | age | address |
+----+------+--------+------+---------+
| 1 | zs | 男 | 18 | 西安 |
| 2 | zs1 | 女 | 18 | NULL |
| 3 | zs2 | 女 | 18 | NULL |
+----+------+--------+------+---------+
3 rows in set (0.00 sec)3.1truncate指令
该指令也可以删除数据，注意：这种数据删除不通过数据字典，是无法恢复的，请慎用！！！！
主要使用场景：清除测试数据！！！！
mysql> truncate db_info;
Query OK, 0 rows affected (0.02 sec)mysql> select *from db_info;
Empty set (0.01 sec)mysql> desc db_info;
+---------+--------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+---------+--------------+------+-----+---------+-------+
| id | int | NO | PRI | NULL | |
| name | varchar(255) | NO | | NULL | |
| gender | char(1) | YES | | NULL | |
| age | int | YES | | 18 | |
| address | varchar(255) | YES | | NULL | |
+---------+--------------+------+-----+---------+-------+
5 rows in set (0.00 sec)mysql> insert into db_info values(1,"张三","男",18,"西安");
Query OK, 1 row affected (0.00 sec)mysql> select * from db_info;
+----+--------+--------+------+---------+
| id | name | gender | age | address |
+----+--------+--------+------+---------+
| 1 | 张三 | 男 | 18 | 西安 |
+----+--------+--------+------+---------+
1 row in set (0.00 sec)mysql> insert into db_info values(2,"离李四","男",18,"西安");
Query OK, 1 row affected (0.01 sec)mysql> insert into db_info values(三,"王五","男",18,"西安");
ERROR 1054 (42S22): Unknown column '三' in 'field list'
mysql> insert into db_info values(3,"王五","男",18,"西安");
Query OK, 1 row affected (0.01 sec)mysql> insert into db_info values(4,"孙尚香","女",18,"西安");
Query OK, 1 row affected (0.01 sec)mysql> insert into db_info values(5,"鲁智深","男",18,"西安");
Query OK, 1 row affected (0.01 sec)mysql> select* from db_info;
+----+-----------+--------+------+---------+
| id | name | gender | age | address |
+----+-----------+--------+------+---------+
| 1 | 张三 | 男 | 18 | 西安 |
| 2 | 离李四 | 男 | 18 | 西安 |
| 3 | 王五 | 男 | 18 | 西安 |
| 4 | 孙尚香 | 女 | 18 | 西安 |
| 5 | 鲁智深 | 男 | 18 | 西安 |
+----+-----------+--------+------+---------+
5 rows in set (0.00 sec)四： 增加数据
4.1update指令
update 表名称 set 字段名称=新的值 [,字段=xxx [,……] [where 条件];mysql> update db_info set age=44 where id=1;
Query OK, 1 row affected (0.00 sec)
Rows matched: 1 Changed: 1 Warnings: 0mysql> update db_info set age=55 where id="2";
Query OK, 1 row affected (0.01 sec)
Rows matched: 1 Changed: 1 Warnings: 0mysql> select * from db_info;
+----+-----------+--------+------+---------+
| id | name | gender | age | address |
+----+-----------+--------+------+---------+
| 1 | 张三 | 男 | 44 | 西安 |
| 2 | 离李四 | 男 | 55 | 西安 |
| 3 | 王五 | 男 | 18 | 西安 |
| 4 | 孙尚香 | 女 | 18 | 西安 |
| 5 | 鲁智深 | 男 | 18 | 西安 |
+----+-----------+--------+------+---------+
5 rows in set (0.00 sec)mysql> update db_info set age = age+1;
Query OK, 5 rows affected (0.00 sec)
Rows matched: 5 Changed: 5 Warnings: 0mysql> select * from db_info;
+----+-----------+--------+------+---------+
| id | name | gender | age | address |
+----+-----------+--------+------+---------+
| 1 | 张三 | 男 | 45 | 西安 |
| 2 | 离李四 | 男 | 56 | 西安 |
| 3 | 王五 | 男 | 19 | 西安 |
| 4 | 孙尚香 | 女 | 19 | 西安 |
| 5 | 鲁智深 | 男 | 19 | 西安 |
+----+-----------+--------+------+---------+
5 rows in set (0.00 sec)mysql> update db_info set address="四川绵阳";
Query OK, 5 rows affected (0.01 sec)
Rows matched: 5 Changed: 5 Warnings: 0mysql> select *from db_info;
+----+-----------+--------+------+--------------+
| id | name | gender | age | address |
+----+-----------+--------+------+--------------+
| 1 | 张三 | 男 | 45 | 四川绵阳 |
| 2 | 离李四 | 男 | 56 | 四川绵阳 |
| 3 | 王五 | 男 | 19 | 四川绵阳 |
| 4 | 孙尚香 | 女 | 19 | 四川绵阳 |
| 5 | 鲁智深 | 男 | 19 | 四川绵阳 |
+----+-----------+--------+------+--------------+
5 rows in set (0.00 sec)4.2replace语句
replace语句结构和insert的语法结构一模一样
replace into 表名称[(字段1 [,字段2, ……])] {values|value}(字段值, [……]) [,()];
注意：replace 的sql语句，是集更新和插入于一体的一个SQL。
如果插入的数据不存在（主键、unqiue修饰的字段），执行insert执行
如果插入的数据存在（主键、unqiue修饰的字段），则先执行删除语句，再执行insert语句。
mysql> replace into db_info(id,name,gender) values(6,"曹操","男");
Query OK, 1 row affected (0.01 sec)mysql> select *from db_info;
+----+-----------+--------+------+--------------+
| id | name | gender | age | address |
+----+-----------+--------+------+--------------+
| 1 | 张三 | 男 | 45 | 四川绵阳 |
| 2 | 离李四 | 男 | 56 | 四川绵阳 |
| 3 | 王五 | 男 | 19 | 四川绵阳 |
| 4 | 孙尚香 | 女 | 19 | 四川绵阳 |
| 5 | 鲁智深 | 男 | 19 | 四川绵阳 |
| 6 | 曹操 | 男 | 18 | NULL |
+----+-----------+--------+------+--------------+
6 rows in set (0.00 sec)mysql> replace into db_info(id,name,gender) values(7,"张飞","男");
Query OK, 1 row affected (0.01 sec)mysql> select *from db_info;
+----+-----------+--------+------+--------------+
| id | name | gender | age | address |
+----+-----------+--------+------+--------------+
| 1 | 张三 | 男 | 45 | 四川绵阳 |
| 2 | 离李四 | 男 | 56 | 四川绵阳 |
| 3 | 王五 | 男 | 19 | 四川绵阳 |
| 4 | 孙尚香 | 女 | 19 | 四川绵阳 |
| 5 | 鲁智深 | 男 | 19 | 四川绵阳 |
| 6 | 曹操 | 男 | 18 | NULL |
| 7 | 张飞 | 男 | 18 | NULL |
+----+-----------+--------+------+--------------+
7 rows in set (0.00 sec)五：查询语句（select）
使用select查询数据库表中的某些数据。
select 语法结构
select {字段|函数|其他} from 表名称 [where]mysql> select 56;
+----+
| 56 |
+----+
| 56 |
+----+
1 row in set (0.00 sec)mysql> select 56+45;
+-------+
| 56+45 |
+-------+
| 101 |
+-------+
1 row in set (0.00 sec)mysql> select 56*45;
+-------+
| 56*45 |
+-------+
| 2520 |
+-------+
1 row in set (0.01 sec)mysql> select 56-45;
+-------+
| 56-45 |
+-------+
| 11 |
+-------+
1 row in set (0.01 sec)mysql> select 56%45;
+-------+
| 56%45 |
+-------+
| 11 |
+-------+
1 row in set (0.00 sec)mysql> select 100+"张三";
+--------------+
| 100+"张三" |
+--------------+
| 100 |
+--------------+
1 row in set, 1 warning (0.01 sec)mysql> select "100"+200-> ;
+-----------+
| "100"+200 |
+-----------+
| 300 |
+-----------+
1 row in set (0.00 sec)mysql> select 100+"200张三";
+-----------------+
| 100+"200张三" |
+-----------------+
| 300 |
+-----------------+
1 row in set, 1 warning (0.00 sec)mysql> select 100+"张三100";
+-----------------+
| 100+"张三100" |
+-----------------+
| 100 |
+-----------------+
1 row in set, 1 warning (0.00 sec)
+----------+
| null + 1 |
+----------+
| NULL |
+----------+
1 row in set (0.01 sec)mysql> select user();
+----------------+
| user() |
+----------------+
| root@localhost |
+----------------+
1 row in set (0.00 sec)mysql> select database();
+------------+
| database() |
+------------+
| db_user |
+------------+
1 row in set (0.00 sec)mysql> select uuid();
+--------------------------------------+
| uuid() |
+--------------------------------------+
| ce2e757d-11de-11ef-8f71-0a0027000012 |
+--------------------------------------+
1 row in set (0.02 sec)mysql> select uuid();
+--------------------------------------+
| uuid() |
+--------------------------------------+
| e4f66188-11de-11ef-8f71-0a0027000012 |
+--------------------------------------+
1 row in set (0.00 sec)mysql> select * from db_info;
+----+-----------+--------+------+--------------+
| id | name | gender | age | address |
+----+-----------+--------+------+--------------+
| 1 | 张三 | 男 | 45 | 四川绵阳 |
| 2 | 离李四 | 男 | 56 | 四川绵阳 |
| 3 | 王五 | 男 | 19 | 四川绵阳 |
| 4 | 孙尚香 | 女 | 19 | 四川绵阳 |
| 5 | 鲁智深 | 男 | 19 | 四川绵阳 |
| 6 | 曹操 | 男 | 18 | NULL |
| 7 | 张飞 | 男 | 18 | NULL |
+----+-----------+--------+------+--------------+
7 rows in set (0.00 sec)mysql> select id,name from db_info;
+----+-----------+
| id | name |
+----+-----------+
| 1 | 张三 |
| 2 | 离李四 |
| 3 | 王五 |
| 4 | 孙尚香 |
| 5 | 鲁智深 |
| 6 | 曹操 |
| 7 | 张飞 |
+----+-----------+
7 rows in set (0.00 sec)mysql> select id from db_info;
+----+
| id |
+----+
| 1 |
| 2 |
| 3 |
| 4 |
| 5 |
| 6 |
| 7 |
+----+
7 rows in set (0.00 sec)5.1查询当前时间
mysql> select now();
+---------------------+
| now() |
+---------------------+
| 2024-05-15 16:14:39 |
+---------------------+
1 row in set (0.00 sec)5.2模糊查询（like）
mysql> show databases;
+--------------------+
| Database |
+--------------------+
| db_classes |
| db_user |
| information_schema |
| mysql |
| performance_schema |
| sys |
+--------------------+
6 rows in set (0.00 sec)5.2.1查询以db_开头的数据库
mysql> show databases like 'db_%';
+-----------------+
| Database (db_%) |
+-----------------+
| db_classes |
| db_user |
+-----------------+
2 rows in set (0.00 sec)
5.2.2查询数据库表中以张开头的信息
mysql> select * from db_info where name like "张%";
+----+--------+--------+------+--------------+
| id | name | gender | age | address |
+----+--------+--------+------+--------------+
| 1 | 张三 | 男 | 45 | 四川绵阳 |
| 7 | 张飞 | 男 | 18 | NULL |
+----+--------+--------+------+--------------+
2 rows in set (0.01 sec)5.2.3查询数据库表中以香结尾的信息
mysql> select * from db_info where name like "%香";
+----+-----------+--------+------+--------------+
| id | name | gender | age | address |
+----+-----------+--------+------+--------------+
| 4 | 孙尚香 | 女 | 19 | 四川绵阳 |
+----+-----------+--------+------+--------------+
1 row in set (0.00 sec)5.2.4查询数据库表中含有“香”的信息
mysql> select * from db_info where name like "%香%";
+----+-----------+--------+------+--------------+
| id | name | gender | age | address |
+----+-----------+--------+------+--------------+
| 4 | 孙尚香 | 女 | 19 | 四川绵阳 |
+----+-----------+--------+------+--------------+
1 row in set (0.00 sec)mysql> select * from db_info where name like "%尚%";
+----+-----------+--------+------+--------------+
| id | name | gender | age | address |
+----+-----------+--------+------+--------------+
| 4 | 孙尚香 | 女 | 19 | 四川绵阳 |
+----+-----------+--------+------+--------------+
1 row in set (0.00 sec)mysql> select * from db_info where name like "%张%";
+----+--------+--------+------+--------------+
| id | name | gender | age | address |
+----+--------+--------+------+--------------+
| 1 | 张三 | 男 | 45 | 四川绵阳 |
| 7 | 张飞 | 男 | 18 | NULL |
+----+--------+--------+------+--------------+
2 rows in set (0.00 sec)mysql> insert into db_info(id,name) values(8,"秀秀");
Query OK, 1 row affected (0.00 sec)mysql> select * from db_info;
+----+-----------+--------+------+--------------+
| id | name | gender | age | address |
+----+-----------+--------+------+--------------+
| 1 | 张三 | 男 | 45 | 四川绵阳 |
| 2 | 离李四 | 男 | 56 | 四川绵阳 |
| 3 | 王五 | 男 | 19 | 四川绵阳 |
| 4 | 孙尚香 | 女 | 19 | 四川绵阳 |
| 5 | 鲁智深 | 男 | 19 | 四川绵阳 |
| 6 | 曹操 | 男 | 18 | NULL |
| 7 | 张飞 | 男 | 18 | NULL |
| 8 | 秀秀 | NULL | 18 | NULL |
+----+-----------+--------+------+--------------+
8 rows in set (0.00 sec)5.3查询名字第二个字为”秀“的信息
mysql> select * from db_info where name like "_秀%";
+----+--------+--------+------+---------+
| id | name | gender | age | address |
+----+--------+--------+------+---------+
| 8 | 秀秀 | NULL | 18 | NULL |
+----+--------+--------+------+---------+
1 row in set (0.00 sec)5.4查询以张开头的信息
mysql> select * from db_info where name like "_秀%";
+----+--------+--------+------+---------+
| id | name | gender | age | address |
+----+--------+--------+------+---------+
| 8 | 秀秀 | NULL | 18 | NULL |
+----+--------+--------+------+---------+
1 row in set (0.00 sec)5.5查询以深结尾的信息
mysql> select * from db_info where name regexp "深$";
+----+-----------+--------+------+--------------+
| id | name | gender | age | address |
+----+-----------+--------+------+--------------+
| 5 | 鲁智深 | 男 | 19 | 四川绵阳 |
+----+-----------+--------+------+--------------+
1 row in set (0.00 sec)mysql> select gender from db_info;
+--------+
| gender |
+--------+
| 男 |
| 男 |
| 男 |
| 女 |
| 男 |
| 男 |
| 男 |
| NULL |
+--------+
8 rows in set (0.00 sec)mysql> select distinct gender from db_info;
+--------+
| gender |
+--------+
| 男 |
| 女 |
| NULL |
+--------+
3 rows in set (0.01 sec)mysql> select gender from db_info group by gender;
+--------+
| gender |
+--------+
| 男 |
| 女 |
| NULL |
+--------+
3 rows in set (0.00 sec)六：聚会函数-count
统计数据
select count(id) from user;
select count(gender) from user;
select count(id) from user;
select count(1) from user;
select count(1) from user where gender="男";mysql> use db_user;
Database changed
mysql> select * from db_info;
+----+-----------+--------+------+--------------+
| id | name | gender | age | address |
+----+-----------+--------+------+--------------+
| 1 | 张三 | 男 | 45 | 四川绵阳 |
| 2 | 离李四 | 男 | 56 | 四川绵阳 |
| 3 | 王五 | 男 | 19 | 四川绵阳 |
| 4 | 孙尚香 | 女 | 19 | 四川绵阳 |
| 5 | 鲁智深 | 男 | 19 | 四川绵阳 |
| 6 | 曹操 | 男 | 18 | NULL |
| 7 | 张飞 | 男 | 18 | NULL |
| 8 | 秀秀 | NULL | 18 | NULL |
+----+-----------+--------+------+--------------+
8 rows in set (0.00 sec)mysql> select count(*) from db_info;
+----------+
| count(*) |
+----------+
| 8 |
+----------+
1 row in set (0.01 sec)mysql> select count(gender) from db_info;
+---------------+
| count(gender) |
+---------------+
| 7 |
+---------------+
1 row in set (0.00 sec)mysql> select count(id) from db_info;
+-----------+
| count(id) |
+-----------+
| 8 |
+-----------+
1 row in set (0.00 sec)mysql> select count(1) from db_info;
+----------+
| count(1) |
+----------+
| 8 |
+----------+
1 row in set (0.00 sec)mysql> select count(1) from db_info where gender="男";
+----------+
| count(1) |
+----------+
| 6 |
+----------+
1 row in set (0.01 sec)mysql> select count(1) from db_info where gender="女";
+----------+
| count(1) |
+----------+
| 1 |
+----------+
1 row in set (0.00 sec)mysql> select count(gender),gender from db_info group by gender;
+---------------+--------+
| count(gender) | gender |
+---------------+--------+
| 6 | 男 |
| 1 | 女 |
| 0 | NULL |
+---------------+--------+
3 rows in set (0.00 sec)
mysql> select gender,count(gender) from db_info group by gender having count(gender) > 4;
+--------+---------------+
| gender | count(gender) |
+--------+---------------+
| 男 | 6 |
+--------+---------------+
1 row in set (0.00 sec)mysql> select name from db_info;
+-----------+
| name |
+-----------+
| 张三 |
| 离李四 |
| 王五 |
| 孙尚香 |
| 鲁智深 |
| 曹操 |
| 张飞 |
| 秀秀 |
+-----------+
8 rows in set (0.00 sec)mysql> select * from db_info order by id;
+----+-----------+--------+------+--------------+
| id | name | gender | age | address |
+----+-----------+--------+------+--------------+
| 1 | 张三 | 男 | 45 | 四川绵阳 |
| 2 | 离李四 | 男 | 56 | 四川绵阳 |
| 3 | 王五 | 男 | 19 | 四川绵阳 |
| 4 | 孙尚香 | 女 | 19 | 四川绵阳 |
| 5 | 鲁智深 | 男 | 19 | 四川绵阳 |
| 6 | 曹操 | 男 | 18 | NULL |
| 7 | 张飞 | 男 | 18 | NULL |
| 8 | 秀秀 | NULL | 18 | NULL |
+----+-----------+--------+------+--------------+
8 rows in set (0.00 sec)七：排序 order by 字段 [{asc | desc }]
如果存在排序，必须是在分组之后
select 字段
from 表名
[where 条件]
[group by 字段 [, 字段 [,……]] ]
[having 筛选条件]
order by 字段 [{asc | desc }] [, 字段 [{asc | desc }]]
案例select * from user order by age ;
select * from user order by age desc;
select * from user order by age asc;
select * from user order by age , id desc;
年龄排序 mysql> select * from db_info order by age;
+----+-----------+--------+------+--------------+
| id | name | gender | age | address |
+----+-----------+--------+------+--------------+
| 6 | 曹操 | 男 | 18 | NULL |
| 7 | 张飞 | 男 | 18 | NULL |
| 8 | 秀秀 | NULL | 18 | NULL |
| 3 | 王五 | 男 | 19 | 四川绵阳 |
| 4 | 孙尚香 | 女 | 19 | 四川绵阳 |
| 5 | 鲁智深 | 男 | 19 | 四川绵阳 |
| 1 | 张三 | 男 | 45 | 四川绵阳 |
| 2 | 离李四 | 男 | 56 | 四川绵阳 |
+----+-----------+--------+------+--------------+
8 rows in set (0.00 sec)年龄升序mysql> select * from db_info order by age, id desc;
+----+-----------+--------+------+--------------+
| id | name | gender | age | address |
+----+-----------+--------+------+--------------+
| 8 | 秀秀 | NULL | 18 | NULL |
| 7 | 张飞 | 男 | 18 | NULL |
| 6 | 曹操 | 男 | 18 | NULL |
| 5 | 鲁智深 | 男 | 19 | 四川绵阳 |
| 4 | 孙尚香 | 女 | 19 | 四川绵阳 |
| 3 | 王五 | 男 | 19 | 四川绵阳 |
| 1 | 张三 | 男 | 45 | 四川绵阳 |
| 2 | 离李四 | 男 | 56 | 四川绵阳 |
+----+-----------+--------+------+--------------+
8 rows in set (0.00 sec)mysql> select * from db_info where id>0 group by id order by age, id desc;
+----+-----------+--------+------+--------------+
| id | name | gender | age | address |
+----+-----------+--------+------+--------------+
| 8 | 秀秀 | NULL | 18 | NULL |
| 7 | 张飞 | 男 | 18 | NULL |
| 6 | 曹操 | 男 | 18 | NULL |
| 5 | 鲁智深 | 男 | 19 | 四川绵阳 |
| 4 | 孙尚香 | 女 | 19 | 四川绵阳 |
| 3 | 王五 | 男 | 19 | 四川绵阳 |
| 1 | 张三 | 男 | 45 | 四川绵阳 |
| 2 | 离李四 | 男 | 56 | 四川绵阳 |
+----+-----------+--------+------+--------------+
8 rows in set (0.01 sec)mysql> select * from db_info where id>0 group by id having count(id) = 1 order by age, id desc;
+----+-----------+--------+------+--------------+
| id | name | gender | age | address |
+----+-----------+--------+------+--------------+
| 8 | 秀秀 | NULL | 18 | NULL |
| 7 | 张飞 | 男 | 18 | NULL |
| 6 | 曹操 | 男 | 18 | NULL |
| 5 | 鲁智深 | 男 | 19 | 四川绵阳 |
| 4 | 孙尚香 | 女 | 19 | 四川绵阳 |
| 3 | 王五 | 男 | 19 | 四川绵阳 |
| 1 | 张三 | 男 | 45 | 四川绵阳 |
| 2 | 离李四 | 男 | 56 | 四川绵阳 |
+----+-----------+--------+------+--------------+
8 rows in set (0.00 sec)mysql> sclect count(*) from db_info;八：别名的使用
别名（alias ），就是将原有名称，重新赋予一个新的名称
在查询SQL时，可以将查询的结果重新设置名称（字段、表名称）。
字段 as 别名 ，as可以省略select count(*) as count from user;
select count(*) count from user;mysql> select count(*) as count from db_info;
+-------+
| count |
+-------+
| 8 |
+-------+
1 row in set (0.00 sec)mysql> select count(*) count from db_info;
+-------+
| count |
+-------+
| 8 |
+-------+
1 row in set (0.00 sec)mysql> select id, name, age from db_info where id<6;
+----+-----------+------+
| id | name | age |
+----+-----------+------+
| 1 | 张三 | 45 |
| 2 | 离李四 | 56 |
| 3 | 王五 | 19 |
| 4 | 孙尚香 | 19 |
| 5 | 鲁智深 | 19 |
+----+-----------+------+
5 rows in set (0.00 sec)mysql> select * from (select id, name, age from db_info where id<6) as t where t.id = 1;
+----+--------+------+
| id | name | age |
+----+--------+------+
| 1 | 张三 | 45 |
+----+--------+------+
1 row in set (0.01 sec)九：分页查询
查询非常多，此时全部展示是不现实的，因此，需要通过分页展示部分数据
注意：不同的关系型数据库，实现分页效果，可能SQL不一样！！！
MySQL使用 limit关键字实现分页！！！
mysql> select * from db_info limit 3;
+----+-----------+--------+------+--------------+
| id | name | gender | age | address |
+----+-----------+--------+------+--------------+
| 1 | 张三 | 男 | 45 | 四川绵阳 |
| 2 | 离李四 | 男 | 56 | 四川绵阳 |
| 3 | 王五 | 男 | 19 | 四川绵阳 |
+----+-----------+--------+------+--------------+
3 rows in set (0.00 sec)mysql> select * from db_info limit 5;
+----+-----------+--------+------+--------------+
| id | name | gender | age | address |
+----+-----------+--------+------+--------------+
| 1 | 张三 | 男 | 45 | 四川绵阳 |
| 2 | 离李四 | 男 | 56 | 四川绵阳 |
| 3 | 王五 | 男 | 19 | 四川绵阳 |
| 4 | 孙尚香 | 女 | 19 | 四川绵阳 |
| 5 | 鲁智深 | 男 | 19 | 四川绵阳 |
+----+-----------+--------+------+--------------+
5 rows in set (0.00 sec)mysql> select * from db_info limit 0,5;
+----+-----------+--------+------+--------------+
| id | name | gender | age | address |
+----+-----------+--------+------+--------------+
| 1 | 张三 | 男 | 45 | 四川绵阳 |
| 2 | 离李四 | 男 | 56 | 四川绵阳 |
| 3 | 王五 | 男 | 19 | 四川绵阳 |
| 4 | 孙尚香 | 女 | 19 | 四川绵阳 |
| 5 | 鲁智深 | 男 | 19 | 四川绵阳 |
+----+-----------+--------+------+--------------+
5 rows in set (0.00 sec)mysql> select * from db_info limit 5,5;
+----+--------+--------+------+---------+
| id | name | gender | age | address |
+----+--------+--------+------+---------+
| 6 | 曹操 | 男 | 18 | NULL |
| 7 | 张飞 | 男 | 18 | NULL |
| 8 | 秀秀 | NULL | 18 | NULL |
+----+--------+--------+------+---------+
3 rows in set (0.00 sec)C:\Users\GUOGUO>mysql --help
mysql Ver 8.1.0 for Win64 on x86_64 (MySQL Community Server - GPL)
Copyright (c) 2000, 2023, Oracle and/or its affiliates.Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.Usage: mysql [OPTIONS] [database]-?, --help Display this help and exit.-I, --help Synonym for -?--auto-rehash Enable automatic rehashing. One doesn't need to use'rehash' to get table and field completion, but startupand reconnecting may take a longer time. Disable with--disable-auto-rehash.(Defaults to on; use --skip-auto-rehash to disable.)-A, --no-auto-rehashNo automatic rehashing. One has to use 'rehash' to gettable and field completion. This gives a quicker start ofmysql and disables rehashing on reconnect.--auto-vertical-outputAutomatically switch to vertical output mode if theresult is wider than the terminal width.-B, --batch Don't use history file. Disable interactive behavior.(Enables --silent.)--bind-address=name IP address to bind to.--binary-as-hex Print binary data as hex. Enabled by default forinteractive terminals.--character-sets-dir=nameDirectory for character set files.--column-type-info Display column type information.-c, --comments Preserve comments. Send comments to the server. Thedefault is --comments (keep comments), disable with--skip-comments.(Defaults to on; use --skip-comments to disable.)-C, --compress Use compression in server/client protocol.-#, --debug[=#] This is a non-debug version. Catch this and exit.--debug-check This is a non-debug version. Catch this and exit.-T, --debug-info This is a non-debug version. Catch this and exit.-D, --database=name Database to use.--default-character-set=nameSet the default character set.--delimiter=name Delimiter to be used.--enable-cleartext-pluginEnable/disable the clear text authentication plugin.-e, --execute=name Execute command and quit. (Disables --force and historyfile.)-E, --vertical Print the output of a query (rows) vertically.-f, --force Continue even if we get an SQL error.--histignore=name A colon-separated list of patterns to keep statementsfrom getting logged into syslog and mysql history.-G, --named-commandsEnable named commands. Named commands mean this program'sinternal commands; see mysql> help . When enabled, thenamed commands can be used from any line of the query,otherwise only from the first line, before an enter.Disable with --disable-named-commands. This option isdisabled by default.-i, --ignore-spaces Ignore space after function names.--init-command=name SQL Command to execute when connecting to MySQL server.Will automatically be re-executed when reconnecting.--local-infile Enable/disable LOAD DATA LOCAL INFILE.-b, --no-beep Turn off beep on error.-h, --host=name Connect to host.--dns-srv-name=name Connect to a DNS SRV resource-H, --html Produce HTML output.-X, --xml Produce XML output.--line-numbers Write line numbers for errors.(Defaults to on; use --skip-line-numbers to disable.)-L, --skip-line-numbersDon't write line number for errors.-n, --unbuffered Flush buffer after each query.--column-names Write column names in results.(Defaults to on; use --skip-column-names to disable.)-N, --skip-column-namesDon't write column names in results.--sigint-ignore Ignore SIGINT (CTRL-C).-o, --one-database Ignore statements except those that occur while thedefault database is the one named at the command line.-p, --password[=name]Password to use when connecting to server. If password isnot given it's asked from the tty.-,, --password1[=name]Password for first factor authentication plugin.-,, --password2[=name]Password for second factor authentication plugin.-,, --password3[=name]Password for third factor authentication plugin.-W, --pipe Use named pipes to connect to server.-P, --port=# Port number to use for connection or 0 for default to, inorder of preference, my.cnf, $MYSQL_TCP_PORT,/etc/services, built-in default (3306).--prompt=name Set the mysql prompt to this value.--protocol=name The protocol to use for connection (tcp, socket, pipe,memory).-q, --quick Don't cache result, print it row by row. This may slowdown the server if the output is suspended. Doesn't usehistory file.-r, --raw Write fields without conversion. Used with --batch.--reconnect Reconnect if the connection is lost. Disable with--disable-reconnect. This option is enabled by default.(Defaults to on; use --skip-reconnect to disable.)-s, --silent Be more silent. Print results with a tab as separator,each row on new line.--shared-memory-base-name=nameBase name of shared memory.-S, --socket=name The socket file to use for connection.--server-public-key-path=nameFile path to the server public RSA key in PEM format.--get-server-public-keyGet server public key--ssl-mode=name SSL connection mode.--ssl-ca=name CA file in PEM format.--ssl-capath=name CA directory.--ssl-cert=name X509 cert in PEM format.--ssl-cipher=name SSL cipher to use.--ssl-key=name X509 key in PEM format.--ssl-crl=name Certificate revocation list.--ssl-crlpath=name Certificate revocation list path.--tls-version=name TLS version to use, permitted values are: TLSv1.2,TLSv1.3--ssl-fips-mode=nameSSL FIPS mode (applies only for OpenSSL); permittedvalues are: OFF, ON, STRICT--tls-ciphersuites=nameTLS v1.3 cipher to use.--ssl-session-data=nameSession data file to use to enable ssl session reuse--ssl-session-data-continue-on-failed-reuseIf set to ON, this option will allow connection tosucceed even if session data cannot be reused.--tls-sni-servername=nameThe SNI server name to pass to server-t, --table Output in table format.--tee=name Append everything into outfile. See interactive help (\h)also. Does not work in batch mode. Disable with--disable-tee. This option is disabled by default.-u, --user=name User for login if not current user.-U, --safe-updates Only allow UPDATE and DELETE that uses keys.-U, --i-am-a-dummy Synonym for option --safe-updates, -U.-v, --verbose Write more. (-v -v -v gives the table output format).-V, --version Output version information and exit.-w, --wait Wait and retry if connection is down.--connect-timeout=# Number of seconds before connection timeout.--max-allowed-packet=#The maximum packet length to send to or receive fromserver.--net-buffer-length=#The buffer size for TCP/IP and socket communication.--select-limit=# Automatic limit for SELECT when using --safe-updates.--max-join-size=# Automatic limit for rows in a join when using--safe-updates.--show-warnings Show warnings after every statement.-j, --syslog Log filtered interactive commands to syslog. Filtering ofcommands depends on the patterns supplied via histignoreoption besides the default patterns.--plugin-dir=name Directory for client-side plugins.--default-auth=name Default authentication client-side plugin to use.--binary-mode By default, ASCII '\0' is disallowed and '\r\n' istranslated to '\n'. This switch turns off both features,and also turns off parsing of all clientcommands except\C and DELIMITER, in non-interactive mode (for inputpiped to mysql or loaded using the 'source' command).This is necessary when processing output from mysqlbinlogthat may contain blobs.--connect-expired-passwordNotify the server that this client is prepared to handleexpired password sandbox mode.--compression-algorithms=nameUse compression algorithm in server/client protocol.Valid values are any combination of'zstd','zlib','uncompressed'.--zstd-compression-level=#Use this compression level in the client/server protocol,in case --compression-algorithms=zstd. Valid range isbetween 1 and 22, inclusive. Default is 3.--load-data-local-dir=nameDirectory path safe for LOAD DATA LOCAL INFILE to readfrom.--fido-register-factor=nameSpecifies authentication factor, for which registrationneeds to be done.--authentication-oci-client-config-profile=nameSpecifies the configuration profile whose configurationoptions are to be read from the OCI configuration file.Default is DEFAULT.--oci-config-file=nameSpecifies the location of the OCI configuration file.Default for Linux is ~/.oci/config and %HOME/.oci/configon Windows.--telemetry-client Load the telemetry_client plugin.--plugin-authentication-kerberos-client-mode=nameKerberos authentication mode. Valid values: SSPI, GSSAPI.If not specified, default is SSPIDefault options are read from the following files in the given order:
C:\WINDOWS\my.ini C:\WINDOWS\my.cnf C:\my.ini C:\my.cnf D:\mysql8.1.0\mysql-8.1.0-winx64\mysql-8.1.0-winx64\my.ini D:\mysql8.1.0\mysql-8.1.0-winx64\mysql-8.1.0-winx64\my.cnf
The following groups are read: mysql client
The following options may be given as the first argument:
--print-defaults Print the program argument list and exit.
--no-defaults Don't read default options from any option file,except for login file.
--defaults-file=# Only read default options from the given file #.
--defaults-extra-file=# Read this file after the global files are read.
--defaults-group-suffix=#Also read groups with concat(group, suffix)
--login-path=# Read this path from the login file.Variables (--variable-name=value)
and boolean options {FALSE|TRUE} Value (after reading options)
------------------------------------------ -------------------------------
auto-rehash TRUE
auto-vertical-output FALSE
bind-address (No default value)
binary-as-hex FALSE
character-sets-dir (No default value)
column-type-info FALSE
comments TRUE
compress FALSE
database (No default value)
default-character-set utf8mb4
delimiter ;
enable-cleartext-plugin FALSE
vertical FALSE
force FALSE
histignore (No default value)
named-commands FALSE
ignore-spaces FALSE
init-command (No default value)
local-infile FALSE
no-beep FALSE
host (No default value)
dns-srv-name (No default value)
html FALSE
xml FALSE
line-numbers TRUE
unbuffered FALSE
column-names TRUE
sigint-ignore FALSE
port 3306
prompt mysql>
quick FALSE
raw FALSE
reconnect TRUE
shared-memory-base-name (No default value)
socket (No default value)
server-public-key-path (No default value)
get-server-public-key FALSE
ssl-ca (No default value)
ssl-capath (No default value)
ssl-cert (No default value)
ssl-cipher (No default value)
ssl-key (No default value)
ssl-crl (No default value)
ssl-crlpath (No default value)
tls-version (No default value)
tls-ciphersuites (No default value)
ssl-session-data (No default value)
ssl-session-data-continue-on-failed-reuse FALSE
tls-sni-servername (No default value)
table FALSE
user (No default value)
safe-updates FALSE
i-am-a-dummy FALSE
connect-timeout 0
max-allowed-packet 16777216
net-buffer-length 16384
select-limit 1000
max-join-size 1000000
show-warnings FALSE
plugin-dir (No default value)
default-auth (No default value)
binary-mode FALSE
connect-expired-password FALSE
compression-algorithms (No default value)
zstd-compression-level 3
load-data-local-dir (No default value)
fido-register-factor (No default value)
authentication-oci-client-config-profile (No default value)
oci-config-file (No default value)
telemetry-client FALSEC:\Users\GUOGUO>
C:\Users\GUOGUO>
C:\Users\GUOGUO>
C:\Users\GUOGUO>mysql -uroot -p123456;
mysql: [Warning] Using a password on the command line interface can be insecure.
ERROR 1045 (28000): Access denied for user 'root'@'localhost' (using password: YES)C:\Users\GUOGUO>mysql -uroot -p123456
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 13
Server version: 8.1.0 MySQL Community Server - GPLCopyright (c) 2000, 2023, Oracle and/or its affiliates.Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners. Mechanism)
