SQLServer:
select top 10 * from tablename;
select top 10 percent from tablename;
select * from tablename limit 10;
SYBASE:
select top 10 * from tablename;
ORACLE:
oracle中无top命令，可使用以下语句查询前N行记录：
select * from table_name where rownum<=10;
原文：http://www.cnblogs.com/rusking/p/3954747.html