加入两个SQL表，其中一个连接字段被多次使用

Question

我有一个问题链接两个表，其中需要多次连接1个字段。

两个表如下：

Venue_Location_Master

• ID
• LOCATION_NAME
• UNID
• is_warehouse

Bag_Dim

• EVENT_ID
• Bag_type
• bag_id
• label_id
• CREATED_DATE
• created_by_employee
• origin_location_id
• destination_location_id
• composition_id

该表的连接origin_location_id或destination_location_id到Venue_Location_Master.id

我试图构建一个返回查询：

• bag_id
• created_by_employee
• event_name
• origin_location_id
• Venue_Location_Master.location_name（ORIGIN_NAME）
• destination_location_id
• Venue_Location_Master.location_name（DESTINATION_NAME）

我用工会试过，但返回所需的数据，而是跨越两行（见下文）。任何人有任何建议？

SELECT [bag_id], 
[created_date], 
[created_by_employee], 
[origin_location_id], 
ISNULL([venue_location_master].[location_name], 'NULL') AS [origin_location_name], 
[destination_location_id], 
ISNULL([venue_location_master].[location_name], 'NULL') AS [destination_location_name]  
,ISNULL([event_master].[event_name], 'NULL') AS [event_name] 
FROM [variance_cash].[dbo].[Bag_Dim] 
LEFT JOIN [verteda_rts_v4].[dbo].[venue_location_master] 
ON [Bag_Dim].[destination_location_id] = [venue_location_master].[id] 
LEFT JOIN [verteda_rts_v4].[dbo].[event_master] 
ON [Bag_Dim].[event_id] = [event_master].[id] 
WHERE [bag_id] = 'K5334' 

Answer 1

如果使用别名，则可以在同一张表上连接两次。

只要加入正确的领域，这应该做的伎俩。

SELECT 
    [bag_id], 
    [created_date], 
    [created_by_employee], 

    --origin 
    [origin_location_id], 
    --use table alias to get correct origin name 
    ISNULL(origin.[location_name], 'NULL') AS [origin_name], 

    --destination 
    [destination_location_id], 
    --use table alias to get correct destination name 
    ISNULL(destination.[location_name], 'NULL') AS [destination_name], 

    ISNULL([event_master].[event_name], 'NULL') AS [event_name] 
FROM [variance_cash].[dbo].[Bag_Dim] 

--join on destination, alias is... destination 
LEFT JOIN [verteda_rts_v4].[dbo].[venue_location_master] as destination 
     ON [Bag_Dim].[destination_location_id] = destination.[id] 

--join on origin, alias is... origin 
LEFT JOIN [verteda_rts_v4].[dbo].[venue_location_master] as origin 
     ON [Bag_Dim].[origin_location_id] = origin.[id] 

LEFT JOIN [verteda_rts_v4].[dbo].[event_master] 
    ON [Bag_Dim].[event_id] = [event_master].[id] 
WHERE [bag_id] = 'K5334'