Understand the basic syntax of mysql

Create table

create table <表名>(
 <字段名>  类型(长度) not null primary key auto_increment, **主键
 name char(20) not null,  
 sex int(4) not null default &#39;0&#39;, **默认键
 degree double(16,2)
)

Delete table

drop table <表名>;
//情空表
delete from <表名>;

Insert data

insert into <表名> [( <字段名1>[,..<字段名n > ])] values ( 值1 )[, ( 值n )]

Query table

select <字段1，字段2，...> from < 表名 > where < 表达式 >

Query the first few fields of the table

select * from MyClass order by id limit 0,2;

Query field sum

select sum('field name') from table name

Query fields are arranged in ascending order and descending order

Descending order:select * from table name where expression order by field name desc

ascending order:select * from table name where Putout=true order by time asc

delete table

delete from 表名 where 表达式

modify table

update 表名 set 字段=新值,… where 条件

Add table fields

alter table table name add field type other;

<1 Primary key:alter table table name add primary key (field name);

<2 Unique constraints: alter table table name add unique index name (field name);

Delete table field

alter table 表名 drop 字段名

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