学习SQL，抓住最近的配置

Question

我有表：

-Parts- 
ID 
name 

-ReportA- 
ID 
PART_ID 
LOCATION_ID 
GPS_ID 
USER_ID 
VALVE_ID 
DATE 

-ReportB- 
ID 
PART_ID 
LOCATION_ID 
TYPE_ID 
NOTES 
GPS_ID 
DATE 

（1）我想抓住那有一张报告，A或B的所有部分：

SELECT 
    * 
FROM 
    parts 
WHERE 
    id IN (SELECT id FROM reports_a UNION SELECT id FROM reports_b 

完美（1 ）但是现在我需要从最近的报告中获取LOCATION_ID和GPS_ID（即A或B）。

例子：

-Parts- 
1 
Valve 

-ReportA- 
1 
1 
4 
9 
2 
12 
2013-02-01 

-ReportB- 
1 
1 
113 
3 
"Changed part" 
90 
2013-03-27 

所以我需要一个SQL脚本，可以抓住所有的部件和他们的最新位置和GPS标识，上面的结果会产生：

PART_ID = 1 
LOCATION_ID = 113 
GPS_ID = 90 

所以我改变我的SQL从前面的脚本到：

SELECT 
    id AS PART_ID 
    (
     (
      SELECT location_id FROM reports_a ORDER BY date DESC 
      UNION 
      SELECT location_id FROM reports_b ORDER BY date DESC 
     ) 
     ORDER BY 
      date DESC 
     LIMIT 1 
    ) AS LOCATION_ID 
FROM 
    parts 
WHERE 
    id IN (SELECT id FROM reports_a UNION SELECT id FROM reports_b 

但是，我不能按日期排序因为它不是字段返回由联盟？

任何想法??

Answer 1

更新：我似乎误解了质询时，下面的查询获取最新的数据，以供您使用的特定product_id

SELECT 
    id, 
    name, 
    (
     SELECT 
     CONCAT('Location_id: ',location_id, ' gps_id: ', gps_id, ' date: ', `date`) 
     FROM 
     (SELECT `date`,part_id, location_id, gps_id FROM reportA 
     UNION 
     SELECT `date`,part_id, location_id, gps_id FROM reportB 
     ) t 
     WHERE part_id = p.id 
     ORDER BY `date` desc 
     LIMIT 1) 
    as details 
FROM 
    parts p 

SQLFiddle

结构是不正确的，理想情况下，你应该将所有report_data放在单个表格中，其列为report_type可能是A或B