Sql 如果内联表的结果集为空，如何不连接该表或返回空值

我有一个查询，返回多个值，所有值都围绕其“交易类型”（可以是卡/现金/支票）分组。有些值是从内联表生成的

所有内联表都返回一个公共列，我可以使用它将它们连接到一个原始表中

然而，在测试过程中有一种可能性被揭示，一些内联表可能什么也不返回，这破坏了我的查询

例如，一个内联表按事务类型返回今年的总销售额，另一个内联表按事务类型返回去年的总销售额

这两个内联表都按事务类型分组，并按事务类型连接到查询的其余部分

在开发过程中，这一切都运行得很好，但在测试期间，我发现如果我们有一个新部门去年没有销售（每个部门使用一个单独的数据库），那么我去年销售的内联表将不会返回任何结果

但由于我在代码中加入了这些内联表，所以我什么也不加入，查询也不返回任何结果

我尝试在内联表上使用左连接，当有数据时，这个左连接查询也可以正常工作

但是，当一些内联表中没有数据（例如去年没有数据）时，左连接查询将永远运行（我在15分钟时取消了它），但原始查询直接返回所有列，但没有数据

所以我可以看到问题所在，我正试图加入一些可能不存在的事情！有人知道我怎么避开这个吗？在下班回家的路上，我的一个想法是返回一个空值并使用COALESCE将其替换为0，但这对连接没有帮助，所以我回到了#1

我希望我提供了足够的信息

--原始查询--

--使用左联接进行查询--

---

试试这个。这是原始查询的修改版本，使用SQL Server explicit

JOIN

语法：

您的原始left join版本的性能问题可能是由于查询缓存造成的-我怀疑这两个版本都非常慢，但您一直在运行第一个版本，因此缓存了结果。您运行了第二个，但没有可从中提取的缓存结果

使用

内部联接

时，如果可能存在

NULL

s，则始终会出现问题，因此需要使用

左联接

。如果它仍然永远运行，您需要检查执行计划并查看发生了什么

declare @ToDate datetime,
        @FromDate datetime,
        @StartYear datetime,
        @Active datetime



set @ToDate = '30-nov-2010'
set @FromDate = '1-Jan-2010'
set @StartYear = '1-jan-2010'
set @active = '1-jan-2010'

select      SUM(th.total_net_retail_central) as 'Net Purchases  TY', 
            IL2.total_sum as 'Net Purchases LY',
            IL3.total_sum as 'Net Purchases YTD',
            IL6.total_sum as 'Net Purchases YTD (LY)',
            tt.Transaction_type_description as 'Channel',
            COUNT(DISTINCT th.customer_id) as 'Number of Customers TY',
            IL7.total_sum as 'Number of Customers LY',
            IL1.Active as 'Number of Active Customers TY',
            COUNT(th.transaction_id) as 'Number of Transactions TY',
            IL8.total_sum as 'Number of Transactions LY',
            IL4.total_sum as 'Total Number of Units TY',
            IL5.total_sum as 'Total Number of Units LY'

FROM        

transaction_header th

LEFT JOIN ( SELECT transaction_type, COUNT(DISTINCT customer_id) as 'Active' 
            from transaction_header  
            where transaction_date BETWEEN @Active and @ToDate 
            group by transaction_type) IL1 ON IL1.transaction_type = th.transaction_type
LEFT JOIN ( SELECT SUM(th.total_net_retail_central) as 'total_sum', th.transaction_type 
            from transaction_header th 
            where th.transaction_date BETWEEN DATEADD(yy, -1, @FromDate) AND  DATEADD(yy, -1, @ToDate) 
            GROUP BY th.transaction_type) IL2 ON IL2.transaction_type = th.transaction_type
LEFT JOIN ( SELECT SUM(th.total_net_retail_central) as 'total_sum', th.transaction_type 
            FROM transaction_header th 
            where th.transaction_date BETWEEN @StartYear AND GETDATE() 
            GROUP BY th.transaction_type) IL3 ON IL3.transaction_type = th.transaction_type
LEFT JOIN ( SELECT SUM(td.quantity) as 'total_sum', th.transaction_type 
            from transaction_detail td, transaction_header th 
            where th.transaction_date BETWEEN @FromDate AND @ToDate AND th.transaction_id = td.transaction_id 
            GROUP BY th.transaction_type) IL4 ON IL4.transaction_type = th.transaction_type
LEFT JOIN ( SELECT SUM(td.quantity) as 'total_sum', th.transaction_type 
            from transaction_detail td, transaction_header th 
            where th.transaction_date BETWEEN DATEADD(yy, -1, @FromDate) AND DATEADD(yy, -1, @ToDate) AND th.transaction_id = td.transaction_id 
            GROUP BY th.transaction_type) IL5 ON IL5.transaction_type = th.transaction_type
LEFT JOIN ( SELECT SUM(th.total_net_retail_central) as 'total_sum', th.transaction_type 
            from transaction_header th 
            where th.transaction_date BETWEEN DATEADD(yy, -1, @StartYear) AND  DATEADD(yy, -1, GETDATE()) 
            GROUP BY th.transaction_type) IL6 ON IL6.transaction_type = th.transaction_type
LEFT JOIN ( SELECT COUNT(DISTINCT th.customer_id) as 'total_sum', th.transaction_type 
            from transaction_header th 
            where th.transaction_date between DATEADD(yy, -1, @FromDate) AND DATEADD(yy, -1, @ToDate) 
            GROUP BY th.transaction_type) IL7 ON IL7.transaction_type = th.transaction_type
LEFT JOIN ( SELECT COUNT(th.customer_id) as 'total_sum', th.transaction_type 
            from transaction_header th 
            where th.transaction_date between DATEADD(yy, -1, @FromDate) AND DATEADD(yy, -1, @ToDate) 
            GROUP BY th.transaction_type) IL8 ON IL8.transaction_type = th.transaction_type
INNER JOIN  transaction_type tt ON th.transaction_type = tt.transaction_type
WHERE 
            th.transaction_date Between @FromDate AND @ToDate
GROUP BY 
            tt.transaction_type_description, IL1.Active, IL2.total_sum, IL3.total_sum, IL4.total_sum, IL5.total_sum, IL6.total_sum, IL7.total_sum, IL8.total_sum

---

试试这个。这是原始查询的修改版本，使用SQL Server explicit

JOIN

语法：

您的原始left join版本的性能问题可能是由于查询缓存造成的-我怀疑这两个版本都非常慢，但您一直在运行第一个版本，因此缓存了结果。您运行了第二个，但没有可从中提取的缓存结果

使用

内部联接

时，如果可能存在

NULL

s，则始终会出现问题，因此需要使用

左联接

。如果它仍然永远运行，您需要检查执行计划并查看发生了什么

declare @ToDate datetime,
        @FromDate datetime,
        @StartYear datetime,
        @Active datetime



set @ToDate = '30-nov-2010'
set @FromDate = '1-Jan-2010'
set @StartYear = '1-jan-2010'
set @active = '1-jan-2010'

select      SUM(th.total_net_retail_central) as 'Net Purchases  TY', 
            IL2.total_sum as 'Net Purchases LY',
            IL3.total_sum as 'Net Purchases YTD',
            IL6.total_sum as 'Net Purchases YTD (LY)',
            tt.Transaction_type_description as 'Channel',
            COUNT(DISTINCT th.customer_id) as 'Number of Customers TY',
            IL7.total_sum as 'Number of Customers LY',
            IL1.Active as 'Number of Active Customers TY',
            COUNT(th.transaction_id) as 'Number of Transactions TY',
            IL8.total_sum as 'Number of Transactions LY',
            IL4.total_sum as 'Total Number of Units TY',
            IL5.total_sum as 'Total Number of Units LY'

FROM        

transaction_header th

LEFT JOIN ( SELECT transaction_type, COUNT(DISTINCT customer_id) as 'Active' 
            from transaction_header  
            where transaction_date BETWEEN @Active and @ToDate 
            group by transaction_type) IL1 ON IL1.transaction_type = th.transaction_type
LEFT JOIN ( SELECT SUM(th.total_net_retail_central) as 'total_sum', th.transaction_type 
            from transaction_header th 
            where th.transaction_date BETWEEN DATEADD(yy, -1, @FromDate) AND  DATEADD(yy, -1, @ToDate) 
            GROUP BY th.transaction_type) IL2 ON IL2.transaction_type = th.transaction_type
LEFT JOIN ( SELECT SUM(th.total_net_retail_central) as 'total_sum', th.transaction_type 
            FROM transaction_header th 
            where th.transaction_date BETWEEN @StartYear AND GETDATE() 
            GROUP BY th.transaction_type) IL3 ON IL3.transaction_type = th.transaction_type
LEFT JOIN ( SELECT SUM(td.quantity) as 'total_sum', th.transaction_type 
            from transaction_detail td, transaction_header th 
            where th.transaction_date BETWEEN @FromDate AND @ToDate AND th.transaction_id = td.transaction_id 
            GROUP BY th.transaction_type) IL4 ON IL4.transaction_type = th.transaction_type
LEFT JOIN ( SELECT SUM(td.quantity) as 'total_sum', th.transaction_type 
            from transaction_detail td, transaction_header th 
            where th.transaction_date BETWEEN DATEADD(yy, -1, @FromDate) AND DATEADD(yy, -1, @ToDate) AND th.transaction_id = td.transaction_id 
            GROUP BY th.transaction_type) IL5 ON IL5.transaction_type = th.transaction_type
LEFT JOIN ( SELECT SUM(th.total_net_retail_central) as 'total_sum', th.transaction_type 
            from transaction_header th 
            where th.transaction_date BETWEEN DATEADD(yy, -1, @StartYear) AND  DATEADD(yy, -1, GETDATE()) 
            GROUP BY th.transaction_type) IL6 ON IL6.transaction_type = th.transaction_type
LEFT JOIN ( SELECT COUNT(DISTINCT th.customer_id) as 'total_sum', th.transaction_type 
            from transaction_header th 
            where th.transaction_date between DATEADD(yy, -1, @FromDate) AND DATEADD(yy, -1, @ToDate) 
            GROUP BY th.transaction_type) IL7 ON IL7.transaction_type = th.transaction_type
LEFT JOIN ( SELECT COUNT(th.customer_id) as 'total_sum', th.transaction_type 
            from transaction_header th 
            where th.transaction_date between DATEADD(yy, -1, @FromDate) AND DATEADD(yy, -1, @ToDate) 
            GROUP BY th.transaction_type) IL8 ON IL8.transaction_type = th.transaction_type
INNER JOIN  transaction_type tt ON th.transaction_type = tt.transaction_type
WHERE 
            th.transaction_date Between @FromDate AND @ToDate
GROUP BY 
            tt.transaction_type_description, IL1.Active, IL2.total_sum, IL3.total_sum, IL4.total_sum, IL5.total_sum, IL6.total_sum, IL7.total_sum, IL8.total_sum

---

我不理解左连接，在那里我可以有空的。但问题是内联表（如IL3）不返回任何内容，因此我有一个从空表到右表中任何内容的左连接。如果我将它们改为右连接，查询会立即运行，但不会得到任何结果。这有意义吗。。如果我使用修改后的查询，它也会“永远”运行。谢谢你的建议。@wesprice-你怎么解释对我来说是没有意义的。如果

LEFT JOIN

到一个没有结果的表，那么这些字段只会得到

NULL

。在我上面的查询中，

transaction\u header

是您的

左侧

表，所有其他的都在

右侧

。如果它们是空的，你仍然应该得到你的

th

字段。。这是忙碌的一周，昨天我的大脑有点疲劳。。我会重新检查我的查询，看看什么是什么，然后让你知道。我不了解左连接，在那里我可以有空的。但问题是内联表（如IL3）不返回任何内容，因此我有一个从空表到右表中任何内容的左连接。如果我将它们改为右连接，查询会立即运行，但不会得到任何结果。这有意义吗。。如果我使用修改后的查询，它也会“永远”运行。谢谢你的建议。@wesprice-你怎么解释对我来说是没有意义的。如果

LEFT JOIN

到一个没有结果的表，那么这些字段只会得到

NULL

。在我上面的查询中，

transaction\u header

是您的

左侧

表，所有其他的都在

右侧

。如果它们是空的，你仍然应该得到你的

th

字段。。这是忙碌的一周，昨天我的大脑有点疲劳。。我会重新检查我的问题，看看是什么，然后让你知道。

declare @ToDate datetime,
        @FromDate datetime,
        @StartYear datetime,
        @Active datetime



set @ToDate = '30-nov-2010'
set @FromDate = '1-Jan-2010'
set @StartYear = '1-jan-2010'
set @active = '1-jan-2010'

select      SUM(th.total_net_retail_central) as 'Net Purchases  TY', 
            IL2.total_sum as 'Net Purchases LY',
            IL3.total_sum as 'Net Purchases YTD',
            IL6.total_sum as 'Net Purchases YTD (LY)',
            tt.Transaction_type_description as 'Channel',
            COUNT(DISTINCT th.customer_id) as 'Number of Customers TY',
            IL7.total_sum as 'Number of Customers LY',
            IL1.Active as 'Number of Active Customers TY',
            COUNT(th.transaction_id) as 'Number of Transactions TY',
            IL8.total_sum as 'Number of Transactions LY',
            IL4.total_sum as 'Total Number of Units TY',
            IL5.total_sum as 'Total Number of Units LY'

FROM        

transaction_header th

LEFT JOIN ( SELECT transaction_type, COUNT(DISTINCT customer_id) as 'Active' 
            from transaction_header  
            where transaction_date BETWEEN @Active and @ToDate 
            group by transaction_type) IL1 ON IL1.transaction_type = th.transaction_type
LEFT JOIN ( SELECT SUM(th.total_net_retail_central) as 'total_sum', th.transaction_type 
            from transaction_header th 
            where th.transaction_date BETWEEN DATEADD(yy, -1, @FromDate) AND  DATEADD(yy, -1, @ToDate) 
            GROUP BY th.transaction_type) IL2 ON IL2.transaction_type = th.transaction_type
LEFT JOIN ( SELECT SUM(th.total_net_retail_central) as 'total_sum', th.transaction_type 
            FROM transaction_header th 
            where th.transaction_date BETWEEN @StartYear AND GETDATE() 
            GROUP BY th.transaction_type) IL3 ON IL3.transaction_type = th.transaction_type
LEFT JOIN ( SELECT SUM(td.quantity) as 'total_sum', th.transaction_type 
            from transaction_detail td, transaction_header th 
            where th.transaction_date BETWEEN @FromDate AND @ToDate AND th.transaction_id = td.transaction_id 
            GROUP BY th.transaction_type) IL4 ON IL4.transaction_type = th.transaction_type
LEFT JOIN ( SELECT SUM(td.quantity) as 'total_sum', th.transaction_type 
            from transaction_detail td, transaction_header th 
            where th.transaction_date BETWEEN DATEADD(yy, -1, @FromDate) AND DATEADD(yy, -1, @ToDate) AND th.transaction_id = td.transaction_id 
            GROUP BY th.transaction_type) IL5 ON IL5.transaction_type = th.transaction_type
LEFT JOIN ( SELECT SUM(th.total_net_retail_central) as 'total_sum', th.transaction_type 
            from transaction_header th 
            where th.transaction_date BETWEEN DATEADD(yy, -1, @StartYear) AND  DATEADD(yy, -1, GETDATE()) 
            GROUP BY th.transaction_type) IL6 ON IL6.transaction_type = th.transaction_type
LEFT JOIN ( SELECT COUNT(DISTINCT th.customer_id) as 'total_sum', th.transaction_type 
            from transaction_header th 
            where th.transaction_date between DATEADD(yy, -1, @FromDate) AND DATEADD(yy, -1, @ToDate) 
            GROUP BY th.transaction_type) IL7 ON IL7.transaction_type = th.transaction_type
LEFT JOIN ( SELECT COUNT(th.customer_id) as 'total_sum', th.transaction_type 
            from transaction_header th 
            where th.transaction_date between DATEADD(yy, -1, @FromDate) AND DATEADD(yy, -1, @ToDate) 
            GROUP BY th.transaction_type) IL8 ON IL8.transaction_type = th.transaction_type
INNER JOIN  transaction_type tt ON th.transaction_type = tt.transaction_type
WHERE 
            th.transaction_date Between @FromDate AND @ToDate
GROUP BY 
            tt.transaction_type_description, IL1.Active, IL2.total_sum, IL3.total_sum, IL4.total_sum, IL5.total_sum, IL6.total_sum, IL7.total_sum, IL8.total_sum