oracle、my sql、sql随机查询语句

1. Oracle,随机查询20条

select * from( select * from 表名 order by dbms_random.value)
where rownum <= 20;

2.SQL Server，随机查询20条

select top 20   * from 表名order by newid()

3.My SQL:，随机查询20条

select * from 表名 order by rand() limit 20