同一个表中,如何写SQL语句查找某一字段重复的记录?

查询C字段有重复的记录吗? 如果是小表可以这样写: select a from tabname where c in (select c from tabname group by c having count(1) >1 ) 大表(需建c列索引): select a from tabname a where exists (select c from tabname b where b.c=a.c group by c having count(1) >1 )