ORACLE:

SELECT * FROM (SELECT * FROM T_USER ORDER BY DBMS_RANDOM.RANDOM()) WHERE RONUM <= 10

MySQL:

SELECT * FROM T_USER  ORDER BY  RAND() LIMIT 10

SQL Server:

SELECT TOP 10 * FROM T_USER ORDER BY NEWID()

Access:

SELECT TOP 10 * FROM T_USER ORDER BY rnd([一个自动编号字段])