1. ORACLE
SELECT * FROM TABLE1 WHERE ROWNUM<=N
2. INFORMIX
SELECT FIRST N * FROM TABLE1
3. DB2
SELECT * ROW_NUMBER() OVER(ORDER BY COL1 DESC) AS ROWNUM WHERE ROWNUM<=N
或者
SELECT COLUMN FROM TABLE FETCH FIRST N ROWS ONLY
4. SQL SERVER
SELECT TOP N * FROM TABLE1
5. SYBASE
SET ROWCOUNT N
GO
SELECT * FROM TABLE1
6. MYSQL
SELECT * FROM TABLE1 LIMIT N
7. FOXPRO
SELECT * TOP N FROM TABLE ORDER BY COLUMN
虽然 select * from table where rownum< 你要查的记录条数，能够取出前几条记录，但是你如果要把排序后记录取前几条结果就不对，如下 SQL 语句select * from table where rownum<50 order by 字段名 desc ，取出来的不时按照先排序后取前几名,而是先取前几名,再排序。
要实现先排序,再取前几名用下面这条语句select * from (select * from table order by 字段名 desc) where rownum<50
某一个字段没有重复的
其他的不要管 只要这条记录重复的情况下的第一条
select * from f where id in (select max(id) from f group by jid)