From e30e6acb787cd259f90dee9ffe043c2c3905f9b3 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=E8=82=96=E9=A3=9E=E9=B9=8F?= <2879562915@qq.com>
Date: Thu, 17 Oct 2024 23:24:51 +0800
Subject: [PATCH 1/3] update

---
 ...\347\273\217\345\205\27050\351\242\230.md" | 36 +++++++++++++++++++
 1 file changed, 36 insertions(+)

diff --git "a/\345\217\266\345\212\237\347\205\247/20241013 Mysql\347\273\217\345\205\27050\351\242\230.md" "b/\345\217\266\345\212\237\347\205\247/20241013 Mysql\347\273\217\345\205\27050\351\242\230.md"
index c876f86..65364e6 100644
--- "a/\345\217\266\345\212\237\347\205\247/20241013 Mysql\347\273\217\345\205\27050\351\242\230.md"	
+++ "b/\345\217\266\345\212\237\347\205\247/20241013 Mysql\347\273\217\345\205\27050\351\242\230.md"	
@@ -442,16 +442,52 @@ select  * from student where s_name like '%风%';
 
 30 查询同名同性的学生名单，并统计同名人数
 
+```sql
+? ? ? ?
+```
+
 31 查询 1990 年出生的学生信息
 
+```sql
+select * from student where s_birth >='1990-01-01';
+```
+
 32 查询每门课程的平均成绩，结果按平均成绩降序排列;平均成绩相同时，按课程编号 c_id 升序排列
 
+```sql
+with -- CTE 
+a as (select c_id,avg(s_score) 平均成绩 from score group by c_id order by avg(s_score) desc) -- 平均成绩不相同时
+select c_name,a.平均成绩 from course,a where a.c_id=course.c_id;
+-------------------------------------------------------------------------------------------------------------------
+with -- CTE 
+a as (select c_id,avg(s_score) 平均成绩 from score group by c_id order by c_id asc) -- 平均成绩不同时
+select c_name,a.平均成绩 from course,a where a.c_id=course.c_id;
+```
+
 33 查询平均成绩大于等于 85 的所有学生的学号、姓名和平均成绩
 
+```sql
+with -- CTE
+a as (select s_id,avg(s_score) 平均成绩 from score group by s_id having 平均成绩 >= 85)
+select s.s_id,s_name,a.平均成绩 from student s,a where a.s_id = s.s_id;
+```
+
 34 查询课程名称为数学，且分数低于 60 的学生姓名和分数
 
+```sql
+with -- CTE
+a as (select s_id,s_score from score where c_id=(select c_id from course where c_name='数学') and s_score<60) -- 子查询作为列当条件
+select s_name,a.s_score from student s,a where s.s_id = a.s_id;
+```
+
 35 查询所有学生的课程及分数情况
 
+```sql
+with -- CTE
+a as (select student.s_name,score.c_id,score.s_score from score right join student on score.s_id=student.s_id)
+select s_name,c.c_name,a.s_score from  course c right join a on a.c_id=c.c_id; 
+```
+
 36 查询任何一门课程成绩在 70 分以上的姓名、课程名称和分数
 
 37 查询不及格的课程
-- 
Gitee


From c2720e455bff5d047c23471d3b37f415b2179924 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=E5=8F=B6=E5=8A=9F=E7=85=A7?= <3210416196@qq.com>
Date: Fri, 18 Oct 2024 11:42:13 +0800
Subject: [PATCH 2/3] =?UTF-8?q?=E6=8F=90=E4=BA=A4?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

---
 .../20241018 \347\264\242\345\274\225.md"     | 100 ++++++++++++++++++
 1 file changed, 100 insertions(+)
 create mode 100644 "\345\217\266\345\212\237\347\205\247/20241018 \347\264\242\345\274\225.md"

diff --git "a/\345\217\266\345\212\237\347\205\247/20241018 \347\264\242\345\274\225.md" "b/\345\217\266\345\212\237\347\205\247/20241018 \347\264\242\345\274\225.md"
new file mode 100644
index 0000000..c676e08
--- /dev/null
+++ "b/\345\217\266\345\212\237\347\205\247/20241018 \347\264\242\345\274\225.md"	
@@ -0,0 +1,100 @@
+# 笔记
+
+- ## 创建普通索引
+
+  ```sql
+  create index 索引名 on 表名(字段名);
+  ```
+
+- ## 创建联合索引
+
+  ```sql
+  create index 索引名 on 表名(字段名1,字段名2);
+  ```
+
+- ## 查看创建的索引
+
+  ```sql
+  show index from 表名;
+  ```
+
+- ## 查看sql语句使用标记到索引
+
+  ```sql
+  explain sql语句;
+  ```
+
+- ## 删除索引
+
+  ```sql
+  drop index 索引名 from 表名;
+  ```
+
+# 练习与作业
+
+- ### -- 1.给emp分别建立 普通索引和唯一索引
+
+  ```sql
+  create index index_job on emp(job); -- 普通索引
+  create  unique index index_ename on emp(ename); -- 唯一索引
+  ```
+
+- ### -- 2.查询emp表有哪些索引
+
+  ```sql
+  show index from emp;
+  ```
+
+- ### -- 3. 使用有索引的字段进行查询，再查看这条语句是否使用到了索引。
+
+  ```sql
+  explain select * from emp where ename = '甘宁';
+  explain select * from emp where ename like '%甘%'; -- 没有遵循最左原则导致索引失效
+  explain select * from emp where ename like '甘%'; -- 遵循最左原则索引没有失效
+  ```
+
+- ### -- 4. 删除前面建立的两个索引
+
+  ```sql
+  drop index index_ename on emp; 
+  drop index index_job on emp; 
+  ```
+
+- ### -- 5. 选择两个字段添加一个复合索引
+
+  ```sql
+  create index index_ename_job on emp(ename,job);
+  ```
+
+- ### -- 6. 使用复合索引的字段进行查询
+
+  ```sql
+  select * from emp where ename='刘备' and job ='经理';
+  
+  explain select * from emp where ename='刘备' and job ='经理'; -- 查看是否用到复合索引
+  ```
+
+- ### -- 想办法用自己的电脑，生成500万行数据,id,uname,age 尽量随机，并记录时间。
+
+  ```sql
+  create procedure pro_addNumberData(in num int)
+  begin 
+  declare temp_age int;
+  declare temp_ename varchar(255);
+  declare t_num int default 0;
+  a:loop
+  if(t_num >= num) then leave a;
+  end if;
+  select round(rand()*100+1) into temp_age;
+  select MD5(rand()) into temp_ename;
+  insert into cs(uname,age) values(temp_ename,temp_age);
+  set t_num=t_num+1;
+  end loop;
+  end;
+  
+  call pro_addNumberData(5000000);
+  ```
+
+- ### -- 1. 不用索引查询 一次姓名uname /并记录时间
+
+- ### -- 2. 建立索引查询 一次姓名uname /并记录时间
\ No newline at end of file
-- 
Gitee


From 4046cae7060196c69fd078eed641d6084251bb72 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=E8=82=96=E9=A3=9E=E9=B9=8F?= <2879562915@qq.com>
Date: Fri, 18 Oct 2024 17:06:54 +0800
Subject: [PATCH 3/3] =?UTF-8?q?=E6=8F=90=E4=BA=A4?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

---
 .../20241018 \347\264\242\345\274\225.md"              | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git "a/\345\217\266\345\212\237\347\205\247/20241018 \347\264\242\345\274\225.md" "b/\345\217\266\345\212\237\347\205\247/20241018 \347\264\242\345\274\225.md"
index c676e08..d8187af 100644
--- "a/\345\217\266\345\212\237\347\205\247/20241018 \347\264\242\345\274\225.md"	
+++ "b/\345\217\266\345\212\237\347\205\247/20241018 \347\264\242\345\274\225.md"	
@@ -95,6 +95,14 @@
   call pro_addNumberData(5000000);
   ```
 
+  ![image-20241018143520967](https://gitee.com/ygzdegitee/img/raw/master/imgs/202410181435167.png)
+
 - ### -- 1. 不用索引查询 一次姓名uname /并记录时间
 
-- ### -- 2. 建立索引查询 一次姓名uname /并记录时间
\ No newline at end of file
+- ![image-20241018163538978](https://gitee.com/ygzdegitee/img/raw/master/imgs/202410181635127.png)
+
+- ### -- 2. 建立索引查询 一次姓名uname /并记录时间
+
+  ![image-20241018170552284](https://gitee.com/ygzdegitee/img/raw/master/imgs/202410181705337.png)
+
+  ![image-20241018170615526](https://gitee.com/ygzdegitee/img/raw/master/imgs/202410181706572.png)
\ No newline at end of file
-- 
Gitee