如何在 MS Access 中连接多个表

Question

我正在开发一个数据库，其中包含不同国家/地区多个码头的销售点数据。设置了一些表来删除原始 POS 数据，每种货币都有一个表。每种货币都设置在唯一的数据库代码下。我在每个表上运行多个查询。其中一个查询加入了下表“T_BLG”，以按位置代码提取唯一的船长组。

T_BLG

Location Code	Min Boat Length	Max Boat Length	Boat Length Group
AYH	0.00	79.00	0-79
AYH	80.00	120.00	80-120
AYH	121.00	99,999.00	121+
OIP	0.00	100.00	0-100
OIP	101.00	200.00	101-200
OIP	201.00	99,999.00	201+

我能够使用以下语句将查询左连接到 T_BLG。

SELECT q_Step2_AMR.*, 

t_BLG.[Boat Length Group], 

[Database Code] & [HS Boat Code] AS [Unique Vessel ID By DB]

FROM q_Step2_AMR LEFT JOIN t_BLG 

ON q_Step2_AMR.[Location Code] = t_BLG.[Location Code]

WHERE (((q_Step2_AMR.[HS Boat Length 2]) Between [Min Boat Length] And [Max Boat Length]));

最近我有一个请求，要引入 Mega Attribute Length。我为这些条件建立了一个新表，并将该表命名为“T_MEGA”。

T_MEGA

Database Code	Min Boat Length	Max Boat Length	Mega Attribute Length
AMR	0.00	150.00	0-150
AMR	151.00	249.00	151-249
AMR	250.00	99,999.00	250+
PCM	0.00	150.00	0-150
PCM	151.00	249.00	151-249
PCM	250.00	99,999.00	250+

下面是我想要的输出，前四个字段是 q_Step2_AMR：

Location Code	Database Code	HS Boat Code	HS Boat Length 2	Unique Vessel ID by DB	Boat Length Group	Mega Attribute Length
AYH	AMR	A0001	50.00	AMRA0001	0-79	0-150
OIP	PCM	A0002	500.00	PCMA0002	201+	250+

我可以按如下方式使用 UNION ALL：

SELECT q_Step2_AMR.*, t_BLG.[Boat Length Group], 
[Database Code] & [HS Boat Code] AS [Unique Vessel ID By DB]
FROM 
q_Step2_AMR 
LEFT JOIN 
t_BLG 
ON q_Step2_AMR.[Location Code] = t_BLG.[Location Code]
WHERE (((q_Step2_AMR.[HS Boat Length 2]) Between [Min Boat Length] And [Max Boat Length])) 

UNION ALL SELECT q_Step2_AMR.*, t_MEGA.[Mega Attribute Length],
"" AS [Unique Vessel ID By DB]
FROM 
q_Step2_AMR 
LEFT JOIN 
t_MEGA 
ON q_Step2_AMR.[Database Code] = t_MEGA.[Database Code] 
WHERE (((q_Step2_AMR.[HS Boat Length 2]) Between [Min Boat Length] And [Max Boat Length]));

但是，由于 Union All 在两个 Select 语句中都使用了 q_Step2_AMR，因此我基本上复制了我的数据。有比使用 UNION ALL 更好的选择吗？

Answer 1

您在评论中发布的 UNION ALL 代码不起作用（正如您所指出的），因为两个 SELECTS 具有不同数量的字段。要使其工作，您只需向第二个 SELECT 添加一个额外的常量字段，与字段 [Unique Vessel ID By DB] 具有相同的数据类型，这似乎是一个字符串。因此代码是：

   SELECT q_Step2_AMR.*, t_BLG.[Boat Length Group], [Database Code] & [HS Boat Code] AS [Unique Vessel ID By DB]
   FROM 
      q_Step2_AMR 
   LEFT JOIN 
      t_BLG 
   ON q_Step2_AMR.[Location Code] = t_BLG.[Location Code] 
   WHERE (((q_Step2_AMR.[HS Boat Length 2]) Between [Min Boat Length] And [Max Boat Length])) 

UNION ALL 

   SELECT q_Step3_AMR.*, t_MEGA.[Mega Attribute Length], "" AS [Unique Vessel ID By DB]
   FROM 
      q_Step3_AMR 
   LEFT JOIN 
      t_MEGA 
   ON q_Step3_AMR.[Database Code] = t_MEGA.[Database Code] 
   WHERE (((q_Step3_AMR.[HS Boat Length 2]) Between [Min Boat Length1] And [Max Boat Length1]));