1、模糊查询字段含有的指定的内容 select *from tablename where user like '%指定的字符串%'  

精确的查找  select *from tablename where user substring(user,'指定位置'，‘长度’)==‘指定值’

 

2、查找字段值重复的次数 

SELECT writer,count(*) as totals from tablename  where writer='值' having count(1)>0