如何有效地 SQL 从 MySQL 数据库中选择最新的条目？
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How to efficiently SQL select newest entries from a MySQL database?
提问by skolima
Possible Duplicate:
SQL Query to get latest price
可能重复：
SQL 查询以获取最新价格
I have a database containing stock price history. I want to select most recent prices for every stock that is listed. I know PostreSQL has a DISTINCT ONstatement that would suit ideally here.
我有一个包含股票价格历史的数据库。我想为列出的每只股票选择最近的价格。我知道 PostreSQL 有一个DISTINCT ON语句，非常适合这里。
Table columns are name, closingPriceand date; nameand datetogether form a unique index.
表列是name,closingPrice和date; name并date一起形成唯一索引。
The easiest(and very uneffective) way is
在最简单的（和非常uneffective）的方法是
SELECT * FROM stockPrices s
WHERE s.date =
(SELECT MAX(date) FROM stockPrices si WHERE si.name = s.name);
Much better approach I found is
我发现更好的方法是
SELECT *
FROM stockPrices s JOIN (
SELECT name, MAX(date) AS date
FROM stockPrices si
GROUP BY name
) lastEntry ON s.name = lastEntry.name AND s.date = lastEntry.date;
What would be an efficient way to do this? What indexes should I create?
这样做的有效方法是什么？我应该创建什么索引？
duplicate of:
SQL Query to get latest price
回答by Vinko Vrsalovic
I think that your second approach is very efficient. What's its problem?
我认为您的第二种方法非常有效。它的问题是什么？
You have to add indexes to name and date.
您必须为名称和日期添加索引。
