Question

我的SQL查看查询有问题。我有几个重复的查询，我认为它不应该是这样的。这只是一个较大的一部分：

    WITH auditlogs ([AuditLogId], [OperationCode], [Operation], [Table], [RowId], [Timestamp], [UserUid], [UserName], [IpAddress], [OperationSet], [ContextUid], [Field], [OldValue], [NewValue]) AS
    (
        SELECT
            al.[Id] AS [AuditLogId],
            al.[Operation] as [OperationCode],
            CASE al.[Operation]
                WHEN 0 THEN 'New'  
                WHEN 1 THEN 'Update'  
                WHEN 2 THEN 'Delete'  
                ELSE 'Warning'  
            END  AS [Operation],
            al.[EntityName] AS [Table],
            CASE al.[EntityId] 
                WHEN -1 THEN NULL
                ELSE al.[EntityId] 
            END AS [RowId],
            al.[Timestamp],
            al.[UserUid],
            al.[UserName],
            al.[IpAddress],
            al.[OperationSet],
            al.[ContextUid],
            alf.[Name],
            alf.[OldValue],
            alf.[NewValue]
        FROM [AuditLog] AS al
            INNER JOIN [AuditLogField] AS alf ON alf.AuditLogId = al.Id
    )
    SELECT [AuditLogId], --- ATTACHUSERS
        [OperationCode], [Operation], [Table], [RowId], [Timestamp], alx.[UserUid], [UserName], 
        [IpAddress], [OperationSet], [ContextUid], 'User' AS [Field], null, u.[FirstName] + ' ' + u.[LastName], s.Id
    FROM (
        SELECT [AuditLogId],
            [OperationCode], [Operation], [Table], [RowId], [Timestamp], [UserUid], [UserName], 
            [IpAddress], [OperationSet], [ContextUid],
            MAX(case when [Field] = 'UserUid' then [NewValue] end) AS AddedUserUid,
            MAX(case when [Field] = 'TenantId' then [NewValue] end) TenantId
        FROM [auditlogs] AS al
        WHERE al.[Table] = 'TenantUser' AND OperationCode = 0
        GROUP BY [AuditLogId], [OperationCode], [Operation], [Table], [RowId], [Timestamp], al.[UserUid], [UserName], 
            [IpAddress], [OperationSet], [ContextUid]
    ) AS alx
    INNER JOIN [User] AS u ON u.[Uid] = CAST(alx.AddedUserUid AS uniqueidentifier) 
    INNER JOIN [Tenant] AS t ON alx.TenantId = t.Id
    INNER JOIN [Subscription] AS s ON s.TenantId = t.id
UNION ALL
    SELECT al.[AuditLogId], --- DETTACHUSERS
        al.[OperationCode], al.[Operation], al.[Table], al.[RowId], al.[Timestamp], al.[UserUid], al.[UserName], 
        al.[IpAddress], al.[OperationSet], al.[ContextUid], 'User' AS [Field], null, u.[FirstName] + ' ' + u.[LastName], s.Id
    FROM [auditlogs] AS al
    INNER JOIN (
        SELECT TOP 1 * 
        FROM (
            SELECT [AuditLogId],
                [OperationCode], [Operation], [Table], [RowId], [Timestamp], [UserUid], [UserName], 
                [IpAddress], [OperationSet], [ContextUid],
                MAX(case when [Field] = 'UserUid' then [NewValue] end) AS AddedUserUid,
                MAX(case when [Field] = 'TenantId' then [NewValue] end) TenantId
            FROM [auditlogs] AS al
            WHERE al.[Table] = 'TenantUser' AND OperationCode = 0
            GROUP BY [AuditLogId], [OperationCode], [Operation], [Table], [RowId], [Timestamp], al.[UserUid], [UserName], 
                [IpAddress], [OperationSet], [ContextUid]
        ) AS added
        ORDER BY [Timestamp] DESC
    ) AS alx ON alx.RowId = al.RowId AND al.OperationCode = 2
    INNER JOIN [User] AS u ON u.[Uid] = CAST(alx.AddedUserUid AS uniqueidentifier) 
    INNER JOIN [Tenant] AS t ON alx.TenantId = t.Id
    INNER JOIN [Subscription] AS s ON s.TenantId = t.id

我知道我的视图可以由其他人组成，我的意思是，将它分成几个较小的视图，以便重用它们并避免重复的部分。但是，我想知道这是否是一个很好的方法，或者是否有另一种更好的方法。

拆分它，是最好的解决方案吗？

Answer 1

CTE是在查询中重构代码的一种非常好的方法。

只需注意一点：这不会影响性能。 SQL Server仍然分别优化每个引用，无论好坏（在我看来）。这是微软的一个已知问题，他们甚至撰写了有关它的白皮书。例如，Here是对此优化的正式请求。

作为第二个注释，通常当您将表连接到自身的摘要时，窗口函数将更有效。你的查询相当复杂，所以我不确定这是否会有所帮助。

是的，你可以拥有多个cte。这是一个基本的例子：

with digits as (select 0 as digit union all select 1 as digit),
     digits2 as (select d1.digit + d2.digit*10 as num from digits d1 cross join digits d2)
select *
from digits2

顺便说一下，这可以用来在SQL Server中生成数字序列。

重构查询以避免重复的代码

1 个答案: