MySQL common query statement accumulation

>>Insert an incremental value in a column in MySQL

SET @i := 100;
 UPDATE auge_item_classification SET c_code=(@i:=(@i+1));

>>MySQL query duplicate records

SELECT id,count(id)  count FROM x_table GROUP BY id HAVING count>1

>> insert data from one table into another table

1. 表结构完全一样  
insert into 表1
select * from 表2
2. 表结构不一样（这种情况下得指定列名）  
insert into 表1 (列名1,列名2,列名3)  
select  列1,列2,列3 from 表2