php basics mysql
This article introduces the basics of PHP mysql, which has certain reference value. Now I share it with everyone. Friends in need can refer to it
mysql black window command
set names gbk Set the environment encoding name for connecting to the database (only this one in the black window)
show databases Display the created database list
drop database database name Delete database
create database chenchen Create database "chenchen"
create database chenche charset utf8
use database name use database (enter the database)
show tables Display table
mysql backup and recovery
Backup mysqldump -h localhost -u root -p wp5 > f:/123.sql
Restore
mysql -h localhost -u root -p chenchen1 < f:/123. sql
Create table
Modify table
Add a field
Delete a field
Modify a field
Delete table
# 单行注释
-- 注释内容(--后面带一个空格)
/*
注释内容
*/
delimiter // #设定新的语句结束符
#大小写问题
#-------------------------数据库定义语言 DDL-----------------------------
#创建数据库
create database chenchen charset utf8 collation utf8_general_ci
#显示数据库中的所有可用编码
show charset;
#显示mysql中的所有可用排序规则（utf8_general_ci utf8_bin）
show collation
#删除数据库
drop database if exists chenchen
#修改数据库（字符编码）
alter database chenchen charset utf8 collation utf8_general_ci
#显示所有数据库
show databases
#显示一个数据库的创建语句
show create database chenchen
#选择数据
use chenchen
# 数据(字段)类型：数字 字符型 时间型
#数字 tinyint smallint mediumint int bigint float double decimal
#日期时间 year timestamp time date datetime
#字符串型 set enum blob text varchar char
#常用字段类型 tinyint int float decimal timestamp date datetime set enum text varchar char
# tinyint 1个字节 8位 -128——127 八位一个字节
# int 4个字节 32位
# bigint 8个字节 64位
#整数类型字段的设定形式：类型名 [M] [unsigned] [zerofill] m:显示长度 unsigned：无符号数没有负数 zerofill：0填充
create table tab_int(f1 int,f2 tinyint,f3 bigint);
create table tab_int2(f1 int unsigned,f2 tinyint zerofill,f3 bigint(10) zerofill);
insert into tab_int2 values(1,1,1);
#float 单精度浮点型 4个字节存储数据，精度大约有6到7个有效数字位
#double 双精度浮点型 8个字节存储数据，精度大约只有20个有效数字位
#decimal (定点型)整数部分最长大概有65位，小数部分最长大概有30位，一般设置格式为 decimal(总位数,小数部分位数)
create table tab3(f1 float,f2 double,f3 decimal(10,2));
insert into tab3 values(1.28,100.9999,8888.012);
#字符类型 （用单引号）
#varchar 可变长度，必须定义长度（最多存储字符的个数），最大长度理论值 65535，实际最大值65533 gbk 65533/2 utf8 65533/3
#char 定长字符串，使用时设定其长度，不设定默认长度为1，最大理论长度是255
#enum 单选 enum("选项1","选项2","选项3"); 最多65533个选项 对应数字值 1.2.3.4.......65533
#set 多选 set("选项1","选项2","选项3"); 最多64个选项 对应数字值 1 2 4 8 16
# enum，set写入数据时可以用字符串本身也可以用对应的数字。set可以用对应数字的和。
#text 长文本类型
#其它
#binary 定长二进制字符串 varbinary 不定长二进制字符串 blob 二进制数据类型，存的仍然是二进制值，适用于存储图片、文件等
#时间类型
#datetime 日期时间
#date 日期
#time 时间
#year 年
#timestamp 时间戳（这个字段通常不用赋值）now() md5()
#---------------------表定义-------------------------
create table if not exists tab4(id bigint(20) auto_increment primary key,name varchar(8) ,age int(4) ,phone varchar(12));
# primary key 主键 用于唯一确定一行数据
# unique key 唯一不能重复
# not null 不能为空
# default "xxx" 默认值
# comment 'xxxxxx' 字段说明Related recommendations:
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