Question

我使用Linq2Sql作为ORM并遇到以下问题：我有2个表，我们称之为客户端（id，name）和client_action（id，clientid，date）。 'client'表包含客户端，client_action包含用户操作的日志，我只需要第一个。

有一个linq2sql查询（带分页和排序），导致以下sql：

SELECT TOP (10) /* columns here */
FROM (
    SELECT /* columns here */
    FROM [dbo].[client] AS [t0]
    CROSS APPLY ((
            SELECT NULL AS [EMPTY]
            ) AS [t8]
        OUTER APPLY (
            SELECT [t9].[source]
            FROM [action] AS [t9]
            INNER JOIN (
                SELECT MIN([t10].[actionID]) AS [value], [t10].[ClientID]
                FROM [client_action] AS [t10]
                GROUP BY [t10].[clientID]
                ) AS [t11] ON [t9].[ID] = [t11].[value]
            WHERE [t0].[ID] = [t11].[ClientID]
            ) AS [t12])
    ) AS [t17]
WHERE /* filter for fields from the client table */
ORDER BY [t17].[date_created] DESC

该查询中存在逻辑错误，我更改了它。现在生成的sql如下所示：

SELECT TOP (10) /* columns here */
FROM (
    SELECT /* columns here */
    FROM (
        SELECT /* columns here */
        FROM [dbo].[client] AS [t0]
        CROSS APPLY ((
                SELECT NULL AS [EMPTY]
                ) AS [t3]
            OUTER APPLY (
                SELECT [t7].[value]
                FROM (
                    SELECT [t5].[ClientID], (
                        SELECT TOP (1) [t6].[ID]
                        FROM [client_action] AS [t6]
                        WHERE [t5].[clientID] = [t6].[clientID]
                        ORDER BY [t6].[date_created]
                        ) AS [value]
                    FROM (
                        SELECT [t4].[clientID]
                        FROM [client_action] AS [t4]
                        GROUP BY [t4].[clientID]
                        ) AS [t5]
                    ) AS [t7]
                WHERE [t0].[ID] = [t7].[clientID]
                ) AS [t8])
        LEFT OUTER JOIN [client_action] AS [t9] ON [t8].[value] = [t9].[ID]
        ) AS [t26]
    ) AS [t27]
WHERE /* filter for fields from client table */
ORDER BY [t27].[date_created] DESC

出现性能问题。我使用'SET STATISTICS IO ON'执行了两个查询并获得了有趣的结果：

第一个查询：
- 客户端表已过滤
- '前10名'已应用
- '交叉申请'申请生成的10条记录
表示第二个查询：
- 过滤客户端表（找到大约10K条记录）
- '交叉申请'申请10K记录
- '前10名'已应用

因此它使第二个查询工作得慢得多。有没有办法'调整'查询，以便在过滤后尽可能应用'交叉申请'？

问题在于，有两个'交叉应用'并且有更多的连接，这一切都使得它的工作非常慢。我创建的索引可以提高查询的速度，但仍然足够慢，令人讨厌。

帮助帮助帮助。

如何优化查询

0 个答案: