Question

我正在尝试为SQL Server 2005编写查询，但我无法弄清楚如何执行此操作。我有一个包含以下字段的表：

MessageID int
CategoryID int
优先权tinyint
MessageText NVARCHAR（MAX）

我需要一个查询，它将为类别中具有最高优先级的每一行返回*。例如，如果我有以下数据：

MessageID，CategoryID，Priority，MessageText
1,100,1，错误＃1234发生了 2,100,2，错误＃243发生了 3,100,3，错误＃976发生了 4,200,4，错误＃194发生了 5,200,1，错误＃736发生了 6,300,3，错误＃54发生了 7,300,2，错误＃888发生了

然后结果将是：

MessageID，CategoryID，Priority，MessageText
3,100,3，错误＃976发生了 4,200,4，错误＃194发生了 6,300,3，错误＃54发生了

请注意，它为每个类别返回一行，并且它是该类别具有最高优先级的行。

有谁能告诉我如何编写此查询？

Answer 1

验证

SELECT
    highest_priority_messages.*
FROM
(
    SELECT
    m.MessageID
    , m.CategoryID
    , m.Priority
    , m.MessageText
    , Rank() OVER 
        (PARTITION BY m.CategoryID ORDER BY m.Priority DESC) AS p_rank
    FROM [Message] m
    GROUP BY 
        m.CategoryID 
        , m.Priority
        , m.MessageID
        , m.MessageText
) highest_priority_messages
WHERE 
    p_rank = 1

Answer 2

我认为这应该有用，表名称假定为消息

SELECT
    M.MessageId,
    M.CategoryId,
    M.Priority,
    M.MessageText
FROM 
(
    SELECT 
        CategoryId,
        MAX(Priority) AS Priority
    FROM Messages
    GROUP BY CategoryId
) AS MaxValues
    INNER JOIN Messages M
        ON (MaxValues.CategoryId = M.CategoryId
                AND MaxValues.Priority = M.Priority)

注意

此方法中唯一的“问题”是，如果您有多个最高优先级......

Answer 3

如果你想在没有所有子查询的情况下这样做：

SELECT
     MessageID,
     CategoryID,
     Priority,
     MessageText
FROM
     dbo.Messages M1
LEFT OUTER JOIN dbo.Messages M2 ON
     M2.CategoryID = M1.CategoryID AND
     M2.Priority > M1.Priority
WHERE
     M2.MessageID IS NULL

您可能需要根据处理关系的方式调整查询。你没有这样的例子，所以我不确定。

Answer 4

select distinct query1.* from

(select categoryId,msgText,max(priorityId) as MAX_PRIORITY
 from message
  group by categoryId,msgText
 order by categoryId
) query1,


(select categoryId,max(priorityId) as MAX_PRIORITY
 from message
  group by categoryId
 order by categoryId
) query2

where query1.MAX_PRIORITY = query2.MAX_PRIORITY

order by query1.categoryId

Answer 5

SELECT
    Messages.MessageID
    , Messages.CategoryID
    , Messages.Priority
    , Messages. MessageText
FROM
    Messages
    INNER JOIN
    (
        SELECT 
            CategoryID
            , MAX(Priority) AS Priority
        FROM 
            Messages
        GROUP BY
            CategoryID
    ) AS MaxResults
    ON
        (
            Messages.CategoryID = MaxResults.CategoryID
            AND
            Messages.Priority = MaxResults.Priority
        )

看起来这与上面给出的答案基本相同......使用相同的警告。

虽然这个可以直接使用。

Answer 6

这更短，更容易阅读（imo）。

select ms.*
from 
  messages ms
 ,(
  select ms1.categoryid, max(ms1.priority) as max_priority
  from messages ms1
  group by ms1.categoryid
  ) tmp
where ms.categoryid = tmp.categoryid
  and ms.priority = tmp.max_priority;

Answer 7

我发表评论的排名还不够高，所以我想补充一下cfeduke的解决方案：

SELECT
    highest_priority_messages.*
FROM
(
    SELECT
    m.MessageID
    , m.CategoryID
    , m.Priority
    , m.MessageText
    , Rank() OVER 
        (PARTITION BY m.CategoryID ORDER BY m.Priority DESC, m.MessageID DESC) AS p_rank
    FROM [Message] m
    GROUP BY 
        m.CategoryID 
        , m.Priority
        , m.MessageID
        , m.MessageText
) highest_priority_messages
WHERE 
    p_rank = 1

如果您添加另一个具有优先级3的CategoryID 100消息，原始解决方案将带回2行，通过添加另一个订单条件，我们消除了两个项目排名相同的可能性。

这是我插入的一行的副本来测试它。

insert into [Message] (MessageID, CategoryID, Priority, MessageText)
select 8, 100, 3, 'Error #976-2 occurred'

Answer 8

SELECT DISTINCT CategoryId,PS.Priority,MessageID,MessageText
FROM Priority_Scene PS
JOIN (SELECT MAX(Priority) AS Priority FROM Priority_Scene GROUP BY CategoryId) A
ON A.Priority   = PS.Priority

半棘手的SQL查询

8 个答案: