[英]Select latest data per group from joined tables
我有两个这样的表:
survey:
survey_id | store_code | timestamp
product_stock:
survey_id | product_code | production_month | value
如何根据调查时间戳记并按store_code,product_code和production_month分组以获取最新价值?
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
这样会返回结果
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
并且它需要尽可能快,因为数据库很大
更新 -请再次运行查询
这是我的答案:
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;
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