連接表

Question

我有兩個表是這樣選擇每個組最新數據：

survey: 
survey_id | store_code | timestamp 

product_stock: 
survey_id | product_code | production_month | value 

我怎樣才能獲得最新值的基礎上，調查時間戳與store_code，產品代碼，並production_month分組？

例如，如果我有

survey_id | store_code | timestamp 
1   store_1  2015-04-20 
2   store_1  2015-04-22 
3   store_2  2015-04-21 
4   store_2  2015-04-22 

survey_id | product_code | production_month | value 
1   product_1  2     15 
2   product_1  2     10 
1   product_1  3     20 
1   product_2  2     12 
3   product_2  2     23 
4   product_2  2     17 

它會返回結果這樣

survey_id | store_code | time_stamp | product_code | production_month | value 
2   store_1  2015-04-22 product_1  2     10 
1   store_1  2015-04-20 product_1  3     20 
1   store_1  2015-04-20 product_2  2     12 
4   store_2  2015-04-22 product_2  2     17 

，它必須儘可能快，眼看着數據庫的大小

相當大

Answer 1

已更新 - 請再次運行查詢

這是我的回答：

SELECT survey.survey_id, survey.store_code, survey.timestamp, product_stock.survey_id, product_stock.product_code, product_stock.production_month, product_stock.value 
FROM survey 
INNER JOIN product_stock 
ON survey.survey_id = product_stock.survey_id 
WHERE survey.timestamp = (SELECT MAX(timestamp) 
       FROM survey) 
GROUP BY survey.store_code,product_stock.product_code,product_stock.production_month;