删除数据表中的数据 让主键id 从1开始自增

1 方式1

清空表数据并且将主键自增长从1开始(1.先清空表数据2.在把表的自增长设置为1)

DELETE FROM grade;  

ALTER TABLE grade AUTO_INCREMENT=1;  

方式2

使用truncate清空全部数据主键自增长是从1开始(效率更高)

truncate table "表名字"

删除表中部分数据

delete from table where id>100

插入数据

insert into tablename(id,name,...) values (id,name,...)

INSERT INTO tb_name (field1, field2, ..., fieldn) VAULES(value1, value2, ...,valuen);

可空字段、非空但是含有默认值的字段、自增字段可以不列在字段列表中。

INSERT INTO tb_name VAULES(value1, value2, ...,valuen);

更新数据

update tablename set id=?,name=?... where id=?

UPDATE tb_name SET field1=value1, field2=value2, ..., fieldn=valuen [WHERE condition];

删除一条数据

delete from tablename where id=?
DELETE FROM tb_name [WHERE condition];

查询记录

select * from tablename

SELECT column_name FROM tb_name WHERE condition;

内连接：

SELECT field1, field2, ...,fieldn FROM tb_name1, tb_name2, ..., tb_namen [WHERE condition];

外连接分为左连接和右连接

右连接

SELECT left_field, right_field FROM left_tb_name
LEFT JOIN right_tb_name ON condition;

左连接

SELECT left_field, right_field FROM right_tb_name
LEFT JOIN left_tb_name ON condition;