如何分组，并从两个表中选择，每个给定的 id 需要两条记录答案

【问题标题】：how to group by, and select from two tables, need two records for each given id如何分组，并从两个表中选择，每个给定的 id 需要两条记录
【发布时间】：2013-08-01 17:36:33
【问题描述】：

我是 SQL 查询的新手。您能帮我解决以下问题吗？

表 1 报价观察：

id value quotePointId asOfTime

表 2 报价点：

id, quotoType

quoteType 可以是 LastPrice、RepoRate 等

我需要从表1中选择id和值，asOfTime，quoteType，asOfTime最高，quoteType=LastPrice (=1) or RepoRate (=2)在表2中；我需要返回两条记录，一条为最后价格，一条为每个 id 的回购利率，但最后价格和回购利率都应该是最高的 asOfTime。

我有这个，但它会给出最后价格或回购利率，以 asOfTime 较高者为准。

SELECT QuoteObservations.id, QuoteObservations.value, 
QuoteObservations.quotePointId, max(QuoteObservations.asOfTime) as asOfTime, 
QuoteObservations.dataProviderId, QuotePoints.quoteType 
FROM QuoteObservations, QuotePoints 
WHERE (QuoteObservations.id =1 OR QuoteObservations.id = 2 ) 
AND QuoteObservations.quotePointId = QuotePoints.id 
AND (QuotePoints.quoteType = 1 or QuotePoints.quoteType = 2)
group by QuoteObservations.id, QuoteObservations.value, 
QuoteObservations.quotePointId,QuoteObservations.dataProviderId, QuotePoints.quoteType;

【问题讨论】：

“不工作”一词含糊不清。请更具体。

标签： sql group-by

【解决方案1】：

您需要删除限制QuoteObservations.id =1 OR QuoteObservations.id = 2 上结果的 WHERE 条件

这是修改后的 SQL，删除了该条件。我还将 JOIN 条件移到了 JOIN 子句中。

SELECT  QuoteObservations.id, 
        QuoteObservations.value, 
        QuoteObservations.quotePointId,
        max(QuoteObservations.asOfTime) as asOfTime, 
        QuoteObservations.dataProviderId,
        QuotePoints.quoteType 
FROM    QuoteObservations
INNER JOIN
        QuotePoints 
ON      QuoteObservations.quotePointId = QuotePoints.id 
WHERE   QuotePoints.quoteType in (1,2)
group by 
        QuoteObservations.id, 
        QuoteObservations.value, 
        QuoteObservations.quotePointId,
        QuoteObservations.dataProviderId, 
        QuotePoints.quoteType;

【讨论】：

非常感谢，Declan_k
但我的意思是对于 1 个 id，我需要两个报价，一个最新价格，一个 repo_rate，两者都应该是最新的（asOfTime 最高）
是否需要查询两次，一次为quoteType = 1，一次为quottype = 2，才能得到时间戳最高的最后价格和回购利率？

【解决方案2】：

SELECT
    QuoteObservations.id, 
    QuoteObservations.value, 
    QuoteObservations.asOfTime,
    QuotePoints.quoteType
FROM
    QuoteObservations
    LEFT JOIN QuotePoints
    ON QuoteObservations.quotePointId = QuotePoints.id
WHERE
    QuotePoints.quoteType = 1 
    OR QuotePoints.quoteType = 2
ORDER BY 
    QuoteObservations.asOfTime DESC
LIMIT 1;

【讨论】：

【解决方案3】：

我创建了这个查询，它有效，但我敢打赌，有更好、更有效的方法可以做到这一点，有人可以帮忙吗？

select q.*
from (
            select     QuoteObservations.id, QuoteObservations.value,   QuoteObservations.quotePointId, max(QuoteObservations.asOfTime) as asOfTime, QuoteObservations.dataProviderId, qp.quoteType
            from [QuoteObservations]
            inner join QuotePoints qp
            on qp.id = QuoteObservations.quotePointId
            where quotePointId = 1
            group by QuoteObservations.id, QuoteObservations.value, QuoteObservations.quotePointId, QuoteObservations.dataProviderId
    ) q
inner join (

            select     QuoteObservations.id, QuoteObservations.value, QuoteObservations.quotePointId, max(QuoteObservations.asOfTime) as asOfTime, QuoteObservations.dataProviderId, qp.quoteType
            from [QuoteObservations]
            inner join QuotePoints qp
            on qp.id = QuoteObservations.quotePointId
            where quotePointId = 2
            group by QuoteObservations.id, QuoteObservations.value, QuoteObservations.quotePointId, QuoteObservations.dataProviderId
) p
    on  q.id = p.id
inner join (
            select     QuoteObservations.id, QuoteObservations.value, QuoteObservations.quotePointId, max(QuoteObservations.asOfTime) as asOfTime, QuoteObservations.dataProviderId, qp.quoteType
            from [QuoteObservations]
            inner join QuotePoints qp
            on qp.id = QuoteObservations.quotePointId
            where quotePointId = 10
            group by QuoteObservations.id, QuoteObservations.value, QuoteObservations.quotePointId, QuoteObservations.dataProviderId
) s
    on  s.id = p.id

【讨论】：