From dec9e6d3f98578212336cc1a0477873e588c3069 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=E5=AD=99=E5=85=88=E4=BC=98?= <1967671450@qq.com>
Date: Fri, 18 Oct 2024 16:27:36 +0800
Subject: [PATCH] test

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+# 笔记
+
+```sql
+-- 普通索引
+create index 索引名 on 表名(字段名);-- 括号里可以有多个字段，运行时遵行左边优先
+-- 查询索引
+show index from 表名;
+-- 添加索引(多列)
+alter table 表名 add index 索引名(字段名1,字段名2……);
+-- 删除索引
+drop index 索引名 on 表名;
+-- 在建表时指定索引
+create table 表名(
+id int 
+index 索引名(字段名)
+);
+-- 建立唯一索引（单列）
+create unique index 字段名 on 表名(字段名);
+-- 查看有没有用到索引
+explain + 查询语句;
+```
+
+
+
+
+
+# 练习
+
+```sql
+CREATE DATABASE if not exists emp_mp;
+use emp_mp;
+
+create table if not exists `employee`
+(
+    `eid` int not null auto_increment comment '员工id' primary key,
+    `ename` varchar(20) not null comment '员工名称',
+    `dname` varchar(50) not null comment '部门名称',
+    `hiredate` datetime not null comment '入职日期',
+		`birth` date not null comment '生日',
+    `salary` double null comment '基本薪资',
+		`start_sal` double null comment '入职薪资'
+);
+
+insert into `employee` (`ename`, `dname`, `hiredate`,`birth`, `salary`,`start_sal`) values ('傅嘉熙', '开发部', '2002-08-20 12:00:04','1980-12-10', 9000,6500);
+insert into `employee` (`ename`, `dname`, `hiredate`, `birth`,`salary`,`start_sal`) values ('武晟睿', '开发部', '2002-06-12 13:54:12', '1984-2-5',9500,6000);
+insert into `employee` (`ename`, `dname`, `hiredate`, `birth`,`salary`,`start_sal`) values ('孙弘文', '开发部', '2003-10-16 08:27:06','1979-8-7', 9400,8000);
+insert into `employee` (`ename`, `dname`, `hiredate`,`birth`, `salary`,`start_sal`) values ('潘乐驹', '开发部', '2004-04-22 03:56:11','1980-5-12', 9500,6800);
+insert into `employee` (`ename`, `dname`, `hiredate`,`birth`, `salary`,`start_sal`) values ('潘昊焱', '人事部', '2007-02-24 03:40:02','1987-2-12', 5000,4500);
+insert into `employee` (`ename`, `dname`, `hiredate`,`birth`, `salary`,`start_sal`) values ('沈涛', '人事部', '2012-12-14 09:16:37','1993-4-30', 6000,5500);
+insert into `employee` (`ename`, `dname`, `hiredate`, `birth`,`salary`,`start_sal`) values ('江峻熙', '人事部', '2018-05-12 01:17:48','1990-6-8', 5000,3000);
+insert into `employee` (`ename`, `dname`, `hiredate`,`birth`, `salary`,`start_sal`) values ('陆远航', '人事部', '2018-04-14 03:35:57','1989-11-13', 5500,5000);
+insert into `employee` (`ename`, `dname`, `hiredate`, `birth`,`salary`,`start_sal`) values ('姜煜祺', '销售部', '2020-03-23 03:21:05','1995-1-1', 6000,5500);
+insert into `employee` (`ename`, `dname`, `hiredate`, `birth`,`salary`,`start_sal`) values ('邹明', '销售部', '2015-11-23 23:10:06','1996-2-19', 6800,6000);
+insert into `employee` (`ename`, `dname`, `hiredate`, `birth`,`salary`,`start_sal`) values ('董擎苍', '销售部', '2012-02-12 07:54:32','1985-10-7', 6500,4800);
+insert into `employee` (`ename`, `dname`, `hiredate`,`birth`, `salary`,`start_sal`) values ('钟俊驰', '销售部', '2010-04-10 12:17:06','1981-3-25', 6000,3500);
+
+-- 练习和作业 
+-- 1.给emp分别建立 普通索引和唯一索引
+create index emp_ename on employee(ename);
+CREATE unique index emp_id on employee(eid);
+
+-- 2.查询emp表有哪些索引
+show index from employee;
+
+-- 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。
+explain select * from employee where eid=2;
+
+-- 4. 删除前面建立的两个索引
+drop index emp_ename on employee;
+drop index emp_id on employee;
+
+-- 5. 选择两个字段添加一个复合索引
+CREATE index emp_fh on employee(eid,ename);
+
+-- 6. 使用复合索引的字段进行查询
+select * from employee where eid=3 and ename='孙弘文';
+
+
+```
+
+
+
+# 作业
+
+-- 作业
+-- 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 table suiji(
+id int auto_increment PRIMARY key,
+uname VARCHAR(255) not null,
+age int not null
+);
+
+select now();-- 开始的时间
+create procedure wbw()
+begin 
+  DECLARE i int default 0;
+  while i<5000000 do 
+  insert into suiji(uname,age) values 
+  (
+  concat('user',i),
+  floor(rand()*100)
+  );
+	set i=i+1;
+	end while;
+	
+end;
+call wbw();
+
+
+```
+
+![22042e1268f92757c5046da3fe7b13c](https://gitee.com/sxy20031002/picture-bed-warehouse/raw/master/imgss/202410181608978.png)
+
+-- 1. 不用索引查询 一次姓名uname /并记录时间
+
+```sql
+select uname from suiji;
+```
+
+![a52fcdf01240ec58a37278bae281a78](https://gitee.com/sxy20031002/picture-bed-warehouse/raw/master/imgss/202410181608487.png)
+
+-- 2. 建立索引查询 一次姓名uname /并记录时间
+
+```sql
+CREATE index emp_uname on suiji(uname);
+SELECT * from suiji where uname='user22';
+```
+
+![e43a342296e6d9ad34631fc9480d382](https://gitee.com/sxy20031002/picture-bed-warehouse/raw/master/imgss/202410181608461.png)
+
+![cbada65fd5d1eb861aa0d6a84dc41f9](https://gitee.com/sxy20031002/picture-bed-warehouse/raw/master/imgss/202410181609471.png)
-- 
Gitee