php - 从 2 个表中选择记录并排序

Question

我有 2 个表 A 和 B，记录如下

--TABLE A--  
id        date          value  
1        09/01/2012    Reward  
2        09/01/2012    Purchase  
3        07/01/2012    Reward  
4        07/01/2012    Purchase

--TABLE B--  
id   id_from_a     date           value  
1       1         10/01/2012     Generated Rewrd   
2       3         08/01/2012     Generated Reward 

现在我希望结果如下所示

id        date          value  
1         10/01/2012    Generated Reward  
1         09/01/2012    Reward  
2         09/01/2012    Purchase  
3         08/01/2012    Generated Reward  
3         07/01/2012    Reward  
4         07/01/2012    Purchase  

我知道使用 UNIONS 会合并这 2 个表，但我如何像上面提到的那样对其进行排序？

Answer 1

UNION 可以在末尾指定一个 ORDER BY 子句，该子句适用于整个组合结果集。

SELECT id, date, value
    FROM table_A
UNION
SELECT id, date, value
    FROM table_B
ORDER BY id, date DESC

如果您不需要 UNION 操作的重复数据删除功能，UNION ALL 将产生更好的性能。

SELECT id, date, value
    FROM table_A
UNION ALL
SELECT id, date, value
    FROM table_B
ORDER BY id, date DESC