分类： 数据库

发布于

PG建立分区

# 建父表
create table sales_detail (
	product_id int not null,
	price numeric(12,2),
	amount int not null,
	sale_date date not null,
	buyer varchar(40),
	buyer_contarct text
);
# 建子表
create table sales_detail_y2014m01(check (sale_date >= date '2014-01-01' and sale_date < date '2014-02-01')) inherits (sales_detail);
create table sales_detail_y2014m02(check (sale_date >= date '2014-02-01' and sale_date < date '2014-03-01')) inherits (sales_detail);
create table sales_detail_y2014m03(check (sale_date >= date '2014-03-01' and sale_date < date '2014-04-01')) inherits (sales_detail);
create table sales_detail_y2014m04(check (sale_date >= date '2014-04-01' and sale_date < date '2014-05-01')) inherits (sales_detail);
create table sales_detail_y2014m05(check (sale_date >= date '2014-05-01' and sale_date < date '2014-06-01')) inherits (sales_detail);
create table sales_detail_y2014m06(check (sale_date >= date '2014-06-01' and sale_date < date '2014-07-01')) inherits (sales_detail);
create table sales_detail_y2014m07(check (sale_date >= date '2014-07-01' and sale_date < date '2014-08-01')) inherits (sales_detail);
create table sales_detail_y2014m08(check (sale_date >= date '2014-08-01' and sale_date < date '2014-09-01')) inherits (sales_detail);
create table sales_detail_y2014m09(check (sale_date >= date '2014-09-01' and sale_date < date '2014-10-01')) inherits (sales_detail);
create table sales_detail_y2014m10(check (sale_date >= date '2014-10-01' and sale_date < date '2014-11-01')) inherits (sales_detail);
create table sales_detail_y2014m11(check (sale_date >= date '2014-11-01' and sale_date < date '2014-12-01')) inherits (sales_detail);
create table sales_detail_y2014m12(check (sale_date >= date '2014-12-01' and sale_date < date '2015-01-01')) inherits (sales_detail);
# 字表索引
create index sale_detail_y2014m04_sale_date on sales_detail_y2014m01 (sale_date);
create index sale_detail_y2014m02_sale_date on sales_detail_y2014m02 (sale_date);
create index sale_detail_y2014m03_sale_date on sales_detail_y2014m03 (sale_date);
create index sale_detail_y2014m04_sale_date on sales_detail_y2014m04 (sale_date);
create index sale_detail_y2014m05_sale_date on sales_detail_y2014m05 (sale_date);
create index sale_detail_y2014m06_sale_date on sales_detail_y2014m06 (sale_date);
create index sale_detail_y2014m07_sale_date on sales_detail_y2014m07 (sale_date);
create index sale_detail_y2014m08_sale_date on sales_detail_y2014m08 (sale_date);
create index sale_detail_y2014m09_sale_date on sales_detail_y2014m09 (sale_date);
create index sale_detail_y2014m10_sale_date on sales_detail_y2014m10 (sale_date);
create index sale_detail_y2014m12_sale_date on sales_detail_y2014m12 (sale_date);
# 建触发器
CREATE OR REPLACE FUNCTION sale_detail_insert_trigger()
RETURNS TRIGGER AS $$
BEGIN
IF ( NEW.sale_date >= DATE '2014-01-01' AND
NEW. sale_date < DATE '2014-02-01' ) THEN
INSERT INTO sales_detail_y2014m01 VALUES (NEW.*);

ELSIF (NEW.sale_date >= DATE '2014-02-01' AND
NEW.sale_date < DATE '2014-03-01' ) THEN
INSERT INTO sales_detail_y2014m02 VALUES (NEW.*);

ELSIF (NEW.sale_date >= DATE '2014-03-01' AND
NEW.sale_date < DATE '2014-04-01' ) THEN
INSERT INTO sales_detail_y2014m03 VALUES (NEW.*);

ELSIF (NEW.sale_date >= DATE '2014-04-01' AND
NEW.sale_date < DATE '2014-05-01' ) THEN
INSERT INTO sales_detail_y2014m04 VALUES (NEW.*);

ELSIF (NEW.sale_date >= DATE '2014-05-01' AND
NEW.sale_date < DATE '2014-06-01' ) THEN
INSERT INTO sales_detail_y2014m05 VALUES (NEW.*);

ELSIF (NEW.sale_date >= DATE '2014-06-01' AND
NEW.sale_date < DATE '2014-07-01' ) THEN
INSERT INTO sales_detail_y2014m06 VALUES (NEW.*);

ELSIF (NEW.sale_date >= DATE '2014-07-01' AND
NEW.sale_date < DATE '2014-08-01' ) THEN
INSERT INTO sales_detail_y2014m07 VALUES (NEW.*);

ELSIF (NEW.sale_date >= DATE '2014-08-01' AND
NEW.sale_date < DATE '2014-09-01' ) THEN
INSERT INTO sales_detail_y2014m08 VALUES (NEW.*);

ELSIF (NEW.sale_date >= DATE '2014-09-01' AND
NEW.sale_date < DATE '2014-10-01' ) THEN
INSERT INTO sales_detail_y2014m09 VALUES (NEW.*);

ELSIF (NEW.sale_date >= DATE '2014-10-01' AND
NEW.sale_date < DATE '2014-11-01' ) THEN
INSERT INTO sales_detail_y2014m10 VALUES (NEW.*);

ELSIF (NEW.sale_date >= DATE '2014-11-01' AND
NEW.sale_date < DATE '2014-12-01' ) THEN
INSERT INTO sales_detail_y2014m11 VALUES (NEW.*);

ELSIF ( NEW.sale_date >= DATE '2014-12-01' AND
NEW.sale_date < DATE '2015-01-01' ) THEN
INSERT INTO sales_detail_y2014m12 VALUES (NEW.*);

ELSE
RAISE EXCEPTION 'Date out of range. Fix the
sale_detail_insert_trigger () function!';
END IF;
RETURN NULL;
END;
$$
LANGUAGE plpgsql;
CREATE TRIGGER insert_sale_detail_trigger
BEFORE INSERT ON sales_detail
FOR EACH ROW EXECUTE PROCEDURE
sale_detail_insert_trigger ();

# 数据插入：
insert into sales_detail values(1,43.12,1,date '2014-01-02', '李四', '四川yy');
insert into sales_detail values(1,43.12,1,date '2014-02-02', '李四', '四川yy');
insert into sales_detail values(1,43.12,1,date '2014-03-02', '李四', '四川yy');
insert into sales_detail values(1,43.12,1,date '2014-04-02', '李四', '四川yy');
insert into sales_detail values(1,43.12,1,date '2014-05-02', '李四', '四川yy');
insert into sales_detail values(1,43.12,1,date '2014-06-02', '李四', '四川yy');
insert into sales_detail values(1,43.12,1,date '2014-07-02', '李四', '四川yy');
insert into sales_detail values(1,43.12,1,date '2014-08-02', '李四', '四川yy');
insert into sales_detail values(1,43.12,1,date '2014-09-02', '李四', '四川yy');
insert into sales_detail values(1,43.12,1,date '2014-10-02', '李四', '四川yy');
insert into sales_detail values(1,43.12,1,date '2014-11-02', '李四', '四川yy');
insert into sales_detail values(1,43.12,1,date '2014-12-02', '李四', '四川yy');
insert into sales_detail values(1,43.12,1,date '2014-01-02', '李四', '四川yy');

# 数据测试
select * from sales_detail limit 10;

select * from sales_detail_y2014m01 limit 1;

规则实现触发器功能

CREATE RULE sales_detail_insert_y2014m01 AS

ON INSERT TO sales_detail WHERE

( sale_date >= DATE '2014-01-01' AND sale_date < DATE
'2014-02-01' )
DO INSTEAD
INSERT INTO sales_detail_y2014m01 VALUES (NEW.);
CREATE RULE sales_detail_insert_y2014m02 AS
ON INSERT TO sales_detail WHERE
( sale_date >= DATE '2014-02-01' AND sale_date < DATE
'2014-03-01' )
DO INSTEAD
INSERT INTO sales_detail_y2014m01 VALUES (NEW.);
….
CREATE RULE sales_detail_insert_y2014m12 AS
ON INSERT TO sales_detail WHERE
( sale_date >= DATE '2014-12-01' AND sale_date < DATE

'2015-01-01' )

DO INSTEAD

INSERT INTO sales_detail_y2014m12 VALUES (NEW.*);
发布于

case when

建表插入数据
create table score(
 stu_code varchar(8) not null,
 stu_name varchar(8) not null,
 stu_sex int not null,
 stu_score int not null)
 ;
insert into score values('xm','小明',0,88);
insert into score values('xl','小磊',0,55);
insert into score values('xf','小峰',0,45);
insert into score values('xh','小红',0,66);
insert into score values('xn','晓妮',0,77);
insert into score values('xy','小伊',0,99);
SELECT 
SUM (CASE WHEN STU_SEX = 0 THEN 1 ELSE 0 END) AS MALE_COUNT,  --男生数量统计
SUM (CASE WHEN STU_SEX = 1 THEN 1 ELSE 0 END) AS FEMALE_COUNT,  --女生数量统计
SUM (CASE WHEN STU_SCORE >= 60 AND STU_SEX = 0 THEN 1 ELSE 0 END) AS MALE_PASS,  --男生通过人数统计
SUM (CASE WHEN STU_SCORE >= 60 AND STU_SEX = 1 THEN 1 ELSE 0 END) AS FEMALE_PASS  --女生数量统计
FROM score

postgres=# select (case when stu_sex =0 then 1 else 0 end) from thtf_students;

case 

1
1
1
1
1
1

(6 rows)

postgres=# select case when stu_sex =0 then 1 else 0 end from thtf_students;

case 

1
1
1
1
1
1

(6 rows)

发布于

select 学习

关联表

CREATE TABLE class(no int primary key, class_name varchar(40));
INSERT INTO class VALUES(1,'初二(1)班');
INSERT INTO class VALUES(2,'初二(2)班');
INSERT INTO class VALUES(3,'初二(3)班');
INSERT INTO class VALUES(4,'初二(4)班');
CREATE TABLE student(no int primary key, student_name varchar(40), age int, class_no int);
INSERT INTO student VALUES(1, '张三', 14, 1);
INSERT INTO student VALUES(2, '吴二', 15, 1);
INSERT INTO student VALUES(3, '李四', 13, 2);
INSERT INTO student VALUES(4, '吴三', 15, 2);
INSERT INTO student VALUES(5, '王二', 15, 3);
INSERT INTO student VALUES(6, '李三', 14, 3);
INSERT INTO student VALUES(7, '吴二', 15, 4);
INSERT INTO student VALUES(8, '张四', 14, 4);
1、标准
SELECT student_name, class_name FROM student,
class
WHERE student.class_no = class.no;
2、distinct
select distinct student_name, class_no from student, class;
3、
select student_name, class_name from student, class;
oldboy=# select * from student a, class b where a.class_no=b.no and b.class_name='初二(2)班';
 no | student_name | age | class_no | no | class_name 
----+--------------+-----+----------+----+------------
  3 | 李四         |  13 |        2 |  2 | 初二(2)班
  4 | 吴三         |  15 |        2 |  2 | 初二(2)班
(2 rows)

oldboy=# explain analyze select * from student a, class b where a.class_no=b.no and b.class_name='初二(2)班';
                                                   QUERY PLAN                                                   
----------------------------------------------------------------------------------------------------------------
 Hash Join  (cost=17.79..35.25 rows=3 width=212) (actual time=0.020..0.022 rows=2 loops=1)
   Hash Cond: (a.class_no = b.no)
   ->  Seq Scan on student a  (cost=0.00..15.90 rows=590 width=110) (actual time=0.007..0.008 rows=8 loops=1)
   ->  Hash  (cost=17.75..17.75 rows=3 width=102) (actual time=0.008..0.008 rows=1 loops=1)
         Buckets: 1024  Batches: 1  Memory Usage: 9kB
         ->  Seq Scan on class b  (cost=0.00..17.75 rows=3 width=102) (actual time=0.005..0.006 rows=1 loops=1)
               Filter: ((class_name)::text = '初二(2)班'::text)
               Rows Removed by Filter: 3
 Planning Time: 0.080 ms
 Execution Time: 0.038 ms
(10 rows)

oldboy=# explain analyze select * from student where class_no in  (select no from class where class_name='初二(2)班');
                                                 QUERY PLAN                                                 
------------------------------------------------------------------------------------------------------------
 Hash Join  (cost=17.79..35.25 rows=3 width=110) (actual time=0.019..0.021 rows=2 loops=1)
   Hash Cond: (student.class_no = class.no)
   ->  Seq Scan on student  (cost=0.00..15.90 rows=590 width=110) (actual time=0.006..0.007 rows=8 loops=1)
   ->  Hash  (cost=17.75..17.75 rows=3 width=4) (actual time=0.007..0.008 rows=1 loops=1)
         Buckets: 1024  Batches: 1  Memory Usage: 9kB
         ->  Seq Scan on class  (cost=0.00..17.75 rows=3 width=4) (actual time=0.005..0.005 rows=1 loops=1)
               Filter: ((class_name)::text = '初二(2)班'::text)
               Rows Removed by Filter: 3
 Planning Time: 0.089 ms
 Execution Time: 0.038 ms
(10 rows)
发布于

编码学习

#!/usr/bin/env python3
# -*- coding: utf-8 -*-

from urllib import request
import json
from datetime import datetime, timedelta
import time

def get_data():
    url = 'https://search.51job.com/list/070200,000000,0000,00,9,99,java%25E5%25BC%2580%25E5%258F%2591,2,1.html'
    headers = {
        'User-Agent' : 'Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/109.0.0.0 Safari/537.36'
    }
    req = request.Request(url, headers=headers)
    response = request.urlopen(req)
    print('===============', response.getcode(), type(response))
    if response.getcode() == 200:
        # 字节码
        data = response.read()
        print(type(data))
        # 字节码转字符串
        data = data.decode('utf-8')
        print(type(data))
        # print(data)
        with open('index.html', mode='w', encoding='utf-8') as f:
            f.write(data)

if __name__ == '__main__':
    get_data()
发布于

数据库备份

逻辑备份

逻辑备份
mysqldump -A -B --master-data=2 --single-transaction|gzip >/opt/all.sql.gz
恢复
zcat opt/all.sql.gz|mysql
mysqlbinlog mysql-binlog.000008 mysql-bin.000009 >bin.sql
mysql <bin.sql

物理备份

冷备份方式
cp、rsync、tar、scp等复制工具将MySQL数据文件复制成多份。
热备份方式
Xtrabackup

发布于

SQL分类

核心的SQL

DQL 数据查询语句。select

DML数据操作语言。insert、update、delete

DDL数据定义语言。create、drop、alter

DCL数据控制语言。grant、revoke

非核心

TPL事务处理语言。BEGIN TRASACTION COMMIT ROLLBACK

CCL 指针控制语言

发布于

mysql数据

新建数据结构
 CREATE TABLE `tbl_tree` ( 
`id` int(11) NOT NULL AUTO_INCREMENT, 
`parent_id` int(11) DEFAULT NULL, 
`name` varchar(255) DEFAULT NULL, PRIMARY KEY (`id`) 
) ENGINE=InnoDB AUTO_INCREMENT=34 DEFAULT CHARSET=utf8;  
插入数据信息
INSERT INTO `tbl_tree` (`id`, `parent_id`, `name`) VALUES ('1', '0', '家配成品 类'); 
INSERT INTO `tbl_tree` (`id`, `parent_id`, `name`) VALUES ('2', '0', '营销物料 类'); 
INSERT INTO `tbl_tree` (`id`, `parent_id`, `name`) VALUES ('3', '1', '家配'); 
INSERT INTO `tbl_tree` (`id`, `parent_id`, `name`) VALUES ('4', '1', '寝具'); 
INSERT INTO `tbl_tree` (`id`, `parent_id`, `name`) VALUES ('5', '1', '衣百货'); 
INSERT INTO `tbl_tree` (`id`, `parent_id`, `name`) VALUES ('6', '2', '物料'); 
INSERT INTO `tbl_tree` (`id`, `parent_id`, `name`) VALUES ('7', '3', '凳类'); 
INSERT INTO `tbl_tree` (`id`, `parent_id`, `name`) VALUES ('8', '3', '椅类'); 
INSERT INTO `tbl_tree` (`id`, `parent_id`, `name`) VALUES ('9', '3', '床类'); 
INSERT INTO `tbl_tree` (`id`, `parent_id`, `name`) VALUES ('10', '3', '餐椅类'); 
INSERT INTO `tbl_tree` (`id`, `parent_id`, `name`) VALUES ('11', '3', '桌台类'); 
INSERT INTO `tbl_tree` (`id`, `parent_id`, `name`) VALUES ('12', '3', '沙发类'); 
INSERT INTO `tbl_tree` (`id`, `parent_id`, `name`) VALUES ('13', '3', '窗帘类'); 
INSERT INTO `tbl_tree` (`id`, `parent_id`, `name`) VALUES ('14', '3', '茶几类'); 
INSERT INTO `tbl_tree` (`id`, `parent_id`, `name`) VALUES ('15', '3', '床头柜类'); 
INSERT INTO `tbl_tree` (`id`, `parent_id`, `name`) VALUES ('16', '3', '软床类'); 
INSERT INTO `tbl_tree` (`id`, `parent_id`, `name`) VALUES ('17', '3', '按摩护理 类'); 
INSERT INTO `tbl_tree` (`id`, `parent_id`, `name`) VALUES ('18', '3', '其它配套 类'); 
INSERT INTO `tbl_tree` (`id`, `parent_id`, `name`) VALUES ('19', '4', '软床类'); 
INSERT INTO `tbl_tree` (`id`, `parent_id`, `name`) VALUES ('20', '4', '床垫类'); 
INSERT INTO `tbl_tree` (`id`, `parent_id`, `name`) VALUES ('21', '4', '床配类'); 
INSERT INTO `tbl_tree` (`id`, `parent_id`, `name`) VALUES ('22', '4', '床头柜类'); 
INSERT INTO `tbl_tree` (`id`, `parent_id`, `name`) VALUES ('23', '4', '排骨架类'); 
INSERT INTO `tbl_tree` (`id`, `parent_id`, `name`) VALUES ('24', '4', '销售道具'); 
INSERT INTO `tbl_tree` (`id`, `parent_id`, `name`) VALUES ('25', '5', '礼包类'); 
INSERT INTO `tbl_tree` (`id`, `parent_id`, `name`) VALUES ('26', '5', '日用品类'); 
INSERT INTO `tbl_tree` (`id`, `parent_id`, `name`) VALUES ('27', '5', '家居饰品 类');
发布于

windows 安装mysql5.7

#1、在mysql的安装目录中，新建data目录及my.ini#注意事项my.ini文件必须要用ansi的方式编码

#2、编辑my.ini

[mysqld] 
basedir=D:\mysql-5.7.36-winx64
datadir=D:\mysql-5.7.36-winx64\data
port=3306
sql_mode=NO_ENGINE_SUBSTITUTION,STRICT_TRANS_TABLES
character-set-server=utf8
character_set_filesystem=utf8

[client]
default-character-set=utf8
[mysql]
default-character-set=utf8


#3、将D:\mysql-5.7.36-winx64\bin路径添加到path中


#4.初始化数据库D:\mysql-5.7.36-winx64\bin>mysqld –initialize –user=mysql –console


2022-03-30T07:44:01.640992Z 0 [Warning] TIMESTAMP with implicit DEFAULT value is deprecated. Please use –explicit_defaults_for_timestamp server option (see documentation for more details).

2022-03-30T07:44:01.641071Z 0 [Warning] 'NO_ZERO_DATE', 'NO_ZERO_IN_DATE' and 'ERROR_FOR_DIVISION_BY_ZERO' sql modes should be used with strict mode. They will be merged with strict mode in a future release.
2022-03-30T07:44:01.641079Z 0 [Warning] 'NO_AUTO_CREATE_USER' sql mode was not set.
2022-03-30T07:44:02.890183Z 0 [Warning] InnoDB: New log files created, LSN=45790
2022-03-30T07:44:03.350137Z 0 [Warning] InnoDB: Creating foreign key constraint system tables.2022-03-30T07:44:03.496899Z 0 [Warning] No existing UUID has been found, so we assume that this is the first time that this server has been started. Generating a new UUID: 2b9d5b48-affd-11ec-83b7-0250f2000002.
2022-03-30T07:44:03.537576Z 0 [Warning] Gtid table is not ready to be used. Table 'mysql.gtid_executed' cannot be opened.
2022-03-30T07:44:04.828539Z 0 [Warning] A deprecated TLS version TLSv1 is enabled. Please use TLSv1.2 or higher.
2022-03-30T07:44:04.828830Z 0 [Warning] A deprecated TLS version TLSv1.1 is enabled. Please use TLSv1.2 or higher.
2022-03-30T07:44:04.829738Z 0 [Warning] CA certificate ca.pem is self signed.
2022-03-30T07:44:06.375278Z 1 [Note] A temporary password is generated for root@localhost: V8uZTa!8fk.p


#【注意】记录随机生成密码 或 初始采用这条命令：mysqld initialize insecure –user=mysql –console

#5.启动服务mysql服务net start mysql

【帮助指南】

1、netstat -ano|findstr 3306
2、Windows下Mysql5.7忘记root密码的解决方法

  1. 打开第一个cmd窗口执行 net stop mysql57
  2. 在第一个cmd窗口执行 mysqld –defaults-file=”C:\ProgramData\MySQL\MySQL Server 5.7\my.ini” –skip-grant-tables —注意以你的路径为准
  3. 打开第二个cmd窗口执行 mysql -uroot -p 提示输入密码，直接回车（不用输入密码）
  4. 选择数据库：use mysql;
  5. 更新root的密码：update user set authentication_string=password(‘新密码’) where user=’root’ and Host=’localhost’;
  6. 刷新权限：flush privileges;
  7. 退出：quit
  8. 重新登录：mysql -uroot -p 提示输入密码，这时输入密码才能登录。完成！！！
【FQA】mysqld: [ERROR] Found option without preceding group in config file D:\mysql-5.7.36-winx64\my.ini at line 1!
 
没有新建库，需要建立一个库

发布于

mysql 案例

create table student (
id int(4) not null,
name char(20) not null,
age tinyint(2) not null,
dept varchar(16) not null
);

create database sns; use sns; set names gbk; create table `subject_comment_manager` ( `subject_comment_manager_id` bigint(12) not null auto_increment comment ‘主键’, `subject_type` tinyint(2) not null comment ‘素材类型’, `subject_primary_key` varchar(255) not null comment ‘素材主键’, `subject_title` varchar(255) not null comment ‘素材名称’, `edit_user_nick` varchar(64) not null comment ‘修改人’, `edit_user_time` timestamp null default null comment ‘修改时间’, `edit_comment` varchar(255) default null comment ‘修改的理由’, `state` tinyint(1) not null default ‘1’ comment ‘0 代表关闭，1 代表正常’, primary key (`subject_comment_manager_id`), key `IDX_PRIMARYKEY` (`subject_title`(32)), #括号内的32表示对前32个字符做前缀索引。 key `IDX_SUBJECT_TITLE` (`subject_title`(32)), key `index_nick_type` (`edit_user_nick`(32),`subject_type`) #联合索引，此行为新加的，用于给大家讲解的，实际表语句内没有此行。 ) engine=innodb auto_increment=1 default charset=utf8;

=====================联表查询====================
create table student(
Sno int(10) not null comment ‘学号’,
Sname varchar(16) not null comment ‘姓名’,
Ssex char(6) not null comment ‘性别’,
Sage tinyint(2) not null default ‘0’ comment ‘学生年龄’,
Sdept varchar(16) default null comment ‘学生所在系别’,
primary key (Sno),
key index_Sname(Sname)
) engine=innodb auto_increment=1 default charset=utf8;

create table course(
Cno int(10) not null comment ‘课程号’,
Cname varchar(64) not null comment ‘课程名’,
Ccredit tinyint(2) not null comment ‘学分’,
primary key (Cno)
) engine=innodb auto_increment=1 default charset=utf8;

create table SC(
SCid int(12) not null auto_increment comment ‘主键’,
Cno int(10) not null comment ‘课程号’,
Sno int(10) not null comment ‘学号’,
Grade tinyint(2) not null comment ‘学生成绩’,
primary key (SCid)
) engine=innodb default charset=utf8;

随便插入学生数据

insert into student values(0001,’hognzhi’,’male’,30,’jisuanji’),(0002,’wammg’,’male’,30,’jisuanji’) ,(0003,’oldboy’,’male’,28,’wuliu’) ,(0004,’ts’,’male’,29,’jisuanji’) ,(0005,’oldgirl’,’female’,30,’jisuanji’) ,(0006,’yuany’,’female’,22,’nurse’);

insert into course values(1001,’Linuxyunwei’,3),(1002,’Linuxyunwei’,5),(1003,’Linuxyunwei’,4),(1004,’Linuxyunwei’,4),(1001,’Linuxyunwei’,3);

insert into SC(Sno,Cno,Grade) values(0001,1001,4);
insert into SC(Sno,Cno,Grade) values(0001,1002,3);
insert into SC(Sno,Cno,Grade) values(0001,1003,1);
insert into SC(Sno,Cno,Grade) values(0001,1003,6);

insert into SC(Sno,Cno,Grade) values(0002,1001,3);
insert into SC(Sno,Cno,Grade) values(0002,1002,2);
insert into SC(Sno,Cno,Grade) values(0002,1003,2);
insert into SC(Sno,Cno,Grade) values(0002,1003,8);

insert into SC(Sno,Cno,Grade) values(0003,1001,4);
insert into SC(Sno,Cno,Grade) values(0003,1002,4);
insert into SC(Sno,Cno,Grade) values(0003,1003,2);
insert into SC(Sno,Cno,Grade) values(0003,1003,8);

insert into SC(Sno,Cno,Grade) values(0004,1001,1);
insert into SC(Sno,Cno,Grade) values(0004,1002,1);
insert into SC(Sno,Cno,Grade) values(0004,1003,2);
insert into SC(Sno,Cno,Grade) values(0004,1003,3);

insert into SC(Sno,Cno,Grade) values(0005,1001,5);
insert into SC(Sno,Cno,Grade) values(0005,1002,3);
insert into SC(Sno,Cno,Grade) values(0005,1003,2);
insert into SC(Sno,Cno,Grade) values(0005,1003,9);

联表查询
select student.Sno,student.Sname,course.Cname,SC.Grade from student, course, SC where student.Sno=SC.Sno and course.Cno=SC.Cno;
select student.Sno,student.Sname,course.Cname,SC.Grade from student, course, SC where student.Sno=SC.Sno and course.Cno=SC.Cno order by Sno;
在where后面建索引

explain 查询select 查询语句执行计划
就是查询这个语句，能不能走索引？

use oldboy;
drop table test;
create table test(
id int(4) not null auto_increment,
name char(20) not null,
primary key (id)
);

insert into test values(1,’oldboy’),(2,’oldgir’),(3,’inca’),(4,’zuma’),(5,’kaka’);

select * from test where name=’oldboy’;

explain select * from test where name=’oldboy’;

explain select * from test where name=’oldboy’\G;

create index index_name on test(name);

建索引和没有建索引的区别
mysql> explain select * from test where name=’oldboy’\G
* 1. row *
id: 1
select_type: SIMPLE
table: test
type: ALL
possible_keys: NULL
key: NULL
key_len: NULL
ref: NULL
rows: 5
Extra: Using where
1 row in set (0.00 sec)

mysql> create index index_name on test(name);
Query OK, 0 rows affected (0.01 sec)
Records: 0 Duplicates: 0 Warnings: 0

mysql> explain select * from test where name=’oldboy’\G
* 1. row *
id: 1
select_type: SIMPLE
table: test
type: ref
possible_keys: index_name
key: index_name
key_len: 60
ref: const
rows: 1
Extra: Using where; Using index
1 row in set (0.00 sec)