问题描述
这是一个产品表，有几百万条记录.
This is a product table and have few million of records.
我想列出如下记录:
通常我使用:
I want to list record as below:
Normally I use:
SELECT id,
product_name,
store_id
FROM product
GROUP BY store_id
ORDER BY id.
目前有 SQL 性能问题.我需要 SQL 查询来输出这样的结果.
Currently having SQL performance issue. I need SQL query to output result like this.
推荐答案
有很多替代方案可以解决这个问题，我推荐的一个是加入一个单独获取最新 ID (假设对于每个 store_ID，该列都是 AUTO_INCREMENTed).
There are many alternatives to solves this, one which I recommend is to have joined a subquery which separately gets the latest ID (assuming that the column is AUTO_INCREMENTed) for each store_ID.
SELECT a.*
FROM tableName a
INNER JOIN
(
SELECT store_ID, MAX(ID) max_ID
FROM tableName
GROUP BY store_ID
) b ON a.store_ID = b.store_ID AND
a.ID = b.max_ID
- SQLFiddle 演示
为了获得更好的性能，请确保在这些列上有一个索引:ID 和 store_id.
for better performance, be sure to have an index on these columns: ID and store_id.
更新 1
如果你想对每条记录设置限制，请在下面使用，
if you want to have limit for every records, use this below,
SELECT ID, product_Name, store_ID
FROM tableName a
WHERE
(
SELECT COUNT(*)
FROM tableName b
WHERE b.store_ID = a.store_ID AND b.ID >= a.ID
) <= 2;
- SQLFiddle 演示
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