右补0：select RPAD(id,8,'0') as pad from tablename; 

左补0：select LPAD(id,8,'0') as pad from tablename;

字符串连接：update tableName set title=CONCAT(‘abc’,title,’def’) WHERE id=1

字符串截取【一】：select left(title,50) from tablename

字符串截取【二】：

select substring(title,5) as newTitle from tablename

select substring(title,5,100) as newTitle from tablename

字符串截取【三】：select substring_index(title,'@') as newTitle from tablename