MySql按日期对2个或多个表中的列进行排序

我有以下表格：

comments:
id   /   comments    /   date
1        comment1     1389986953
2        comment2     1389986935


topics:
id   /   topics    /   date
1        topic1      1389986930
2        topic2      1389986940

如何从两个表中选择所有行并按日期排序？ 所以它看起来像：

topic1
comment2
topic2
comment1

尝试选择一个联合

参考：

您需要使用UNION ALL组合两个表的结果，然后将其包装以进行排序

SELECT a.type 
FROM   (SELECT comments AS type, 
               date 
        FROM   comments 
        UNION ALL 
        SELECT topics, 
               date 
        FROM   topics) a 
ORDER  BY a.date; 

SELECT a.type 
FROM   (SELECT comments AS type, 
               date 
        FROM   comments 
        UNION ALL 
        SELECT topics, 
               date 
        FROM   topics) a 
ORDER  BY a.date; 

SELECT * FROM
    (SELECT comments AS mergedField, date
    FROM comments
    UNION ALL
    SELECT topics, date
    FROM topics) mergeTable
ORDER BY date ASC