根据同一个表的列值检测要选择的列

Question

我想构建一个查询，该查询根据同一个表的列返回表的不同列。假设一列代表一种物品。

这是我的临时解决方案，我只是结合多个查询的结果。如您所见，我使用“AS”关键字来重命名默认列名称。

SELECT [custom].[dbo].[records].[id] AS "ID",[type_name] AS "Тип записи", [domain_name] AS "Значение", [custom].[dbo].[records].[record_type_id] FROM [custom].[dbo].[records] INNER JOIN [custom].[dbo].[record_type] ON [custom].[dbo].[records].record_type_id = [custom].[dbo].[record_type].id WHERE [custom].[dbo].[records].record_type_id = 1 
union all 
SELECT [custom].[dbo].[records].[id] AS "ID",[type_name] AS "Тип записи", CAST([ip_address] AS nvarchar(15)) AS "Значение", [custom].[dbo].[records].[record_type_id] FROM [custom].[dbo].[records] INNER JOIN [custom].[dbo].[record_type] ON [custom].[dbo].[records].record_type_id = [custom].[dbo].[record_type].id WHERE [custom].[dbo].[records].record_type_id = 2 
union all 
SELECT [custom].[dbo].[records].[id] AS "ID",[type_name] AS "Тип записи", [domain_name] AS "Значение", [custom].[dbo].[records].[record_type_id] FROM [custom].[dbo].[records] INNER JOIN [custom].[dbo].[record_type] ON [custom].[dbo].[records].record_type_id = [custom].[dbo].[record_type].id WHERE [custom].[dbo].[records].record_type_id = 3 
union all 
SELECT [custom].[dbo].[records].[id] AS "ID",[type_name] AS "Тип записи", [mail_domain] AS "Значение", [custom].[dbo].[records].[record_type_id] FROM [custom].[dbo].[records] INNER JOIN [custom].[dbo].[record_type] ON [custom].[dbo].[records].record_type_id = [custom].[dbo].[record_type].id WHERE [custom].[dbo].[records].record_type_id = 4 
union all 
SELECT [custom].[dbo].[records].[id] AS "ID",[type_name] AS "Тип записи", CAST([ip_address] AS nvarchar(15)) AS "Значение", [custom].[dbo].[records].[record_type_id] FROM [custom].[dbo].[records] INNER JOIN [custom].[dbo].[record_type] ON [custom].[dbo].[records].record_type_id = [custom].[dbo].[record_type].id WHERE [custom].[dbo].[records].record_type_id = 5 
union all 
SELECT [custom].[dbo].[records].[id] AS "ID",[type_name] AS "Тип записи", [domain_name] AS "Значение", [custom].[dbo].[records].[record_type_id] FROM [custom].[dbo].[records] INNER JOIN [custom].[dbo].[record_type] ON [custom].[dbo].[records].record_type_id = [custom].[dbo].[record_type].id WHERE [custom].[dbo].[records].record_type_id = 6 
union all 
SELECT [custom].[dbo].[records].[id] AS "ID",[type_name] AS "Тип записи", [service_name] AS "Значение", [custom].[dbo].[records].[record_type_id] FROM [custom].[dbo].[records] INNER JOIN [custom].[dbo].[record_type] ON [custom].[dbo].[records].record_type_id = [custom].[dbo].[record_type].id WHERE [custom].[dbo].[records].record_type_id = 7 

Answer 1

与CASE操作查询会更短

SELECT 
[custom].[dbo].[records].[id] AS "ID", 
[type_name] AS "Тип записи", 

case [custom].[dbo].[records].record_type_id 
when 1 then [domain_name] 
when 2 then ... 
when 7 then [service_name] 
end AS "Значение", 

[custom].[dbo].[records].[record_type_id] 
FROM [custom].[dbo].[records] 
INNER JOIN [custom].[dbo].[record_type] 
ON [custom].[dbo].[records].record_type_id = [custom].[dbo].[record_type].id 
WHERE [custom].[dbo].[records].record_type_id in (1, 2... 7)