常用sql

查询是否存在相同记录：
select  字段a  from (select count(字段a) as cs,字段a as 字段afrom product group by 字段a) b where b.cs>1

select * from product where 字段a='值'

select c.字段a from (select count(字段a) as sn  from product group by 字段a)c where c.sn>1
设置ID自动增长起始值：

创建表的时候就设置： 

CREATE TABLE `Test` (                                                                                 
          `ID` int(11) NOT NULL AUTO_INCREMENT,                                                               
          `class` varchar(2) NOT NULL,                                                                        
          `NAME` varchar(50) NOT NULL,                                                                        
          `SEX` varchar(2) NOT NULL,                                                                          
          PRIMARY KEY (`ID`)                                                                    
        ) ENGINE=MEMORY AUTO_INCREMENT=1000 DEFAULT CHARSET=utf8 CHECKSUM=1 DELAY_KEY_WRITE=1 ROW_FORMAT=DYNAMIC

如果在创建表时没有设置，后来想设置，可以通过修改实现：

alter   table   Test   auto_increment   =   1000;