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第一部分：字符集
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show charset; ---查看mysql支持字符集
1、服务器端
(1)实例级别
vim f
character-set-server=utf8
(2)库级别
create database oldboy charset UTF8;
create database oldboy1 charset gbk;
alter database oldboy charset utf8mb4;
show create database oldboy;
(3)表级别
create table t1 (id int ,name varchar(20)) default charset utf8;
show create table t1;
2、客户端
alter database oldboy CHARACTER SET utf8 collate utf8_general_ci;
alter table t1 CHARACTER SET latin1;
官方定义，修改后的字符集必须是之前字符集的严格超集。
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第二部分：列属性
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1）约束类：
主键 ：
一个表只能有一个，非空并唯一的列可以设置为主键
create table test (id int not null primary key,name varchar(20));
或者
CREATE TABLEtest(
idint(11) NOT NULL,
namevarchar(20) DEFAULT NULL,
PRIMARY KEY (id)
);
如果业务中没有，非空和唯一条件的列。我们可以人为定义一个无关列，最 好是数字列。create table ptab (pid int not null primary key AUTO_INCREMENT,pname varchar(20),page tinyint,pgen enum('M','F'));
非空：
create table teacher (
id int not null primary key ,
name varchar(20) not null ,
state enum('y','n') not null default 'y');
唯一：
create table people (
p_id char(20) not null primary key,
name varchar(20) not null unique ,
age tinyint not null);
非负数
（2）其他
自增长 --- AUTO_INCREMENT
默认值 ---default 'y'
utf8 字符 ---->3字节
utf8mb4 字符 ---->4个字节
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第三部分：元数据获取---Informatica_schema
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什么是元数据？
1、数据库、表对象的一些定义信息都可以把它称之为元数据
2、数据库的一些状态统计
元数据是存放到数据库的系统表（基表）
利用视图批量操作实例：
1.批量备份脚本拼接
vim /etc/f
secure-file-priv=/tmp
mkdir /bak
select concat("mysqldump ", "-uroot", " -p123 ",TABLE_SCHEMA," ",TABLE_NAME," >/bak/",TABLESCHEMA,"",TABLE_NAME,".sql")from information_schema.tables into outfile '/tmp/tabbak.sh';
2.批量创建world 表结构相同的表
创建语句：
CREATE TABLE world.city_0 LIKE world.city;
USE world
SHOW TABLES;
批量操作：
SELECT CONCAT("create ","table ",TABLE_SCHEMA,"."
,TABLE_NAME," "
,"like ",TABLE_SCHEMA,".",TABLE_NAME,"_0")
FROM information_schema.tables
WHERE TABLE_SCHEMA='world';
3.information_schema 企业需求案例
统计数据量
SELECT
CONCAT(table_schema, '.', table_name) AS "Name"
,CONCAT(ROUND(table_rows / 1000, 2), 'K') AS "Rows"
,CONCAT(ROUND(data_length / ( 10241024 ), 2), 'M') AS "Row Size"
,CONCAT(ROUND(index_length / ( 10241024 ), 2), 'M') AS "Index Size"
,CONCAT(ROUND(( data_length + index_length ) / ( 1024 * 1024 ), 2), 'M') AS "Total"
,ROUND(index_length / data_length, 2) "Row / Index Ratio"
FROM information_schema.TABLES
ORDER BY data_length + index_length DESC
LIMIT 10;
等待事件查看
SELECT
r.trx_id waiting_trx_id
,r.trx_mysql_thread_id waiting_thread
,r.trx_query waiting_query
,b.trx_id blocking_trx_id
,b.trx_mysql_thread_id blocking_thread
,b.trx_query blocking_query
FROM information_schema.innodb_lock_waits w
JOIN information_schema.innodb_trx b ON b.trx_id = w.blocking_trx_id
JOIN information_schema.innodb_trx r ON r.trx_id = w.requesting_trx_id;
