T-SQL复制现有列信息

Question

I'm currently creating a SP that will copy information from table a into table b. The problem that I'm facing is that the information that will be copied can be freely defined in table c. So for Example: Table a has the columns test nvarchar(50), test1 nvarchar(79), beta2 nvarchar(80) and id int

In the settings table it is defined that the columns test and test1 should be copied from table a to table b.

I did include a check if the column already exists. It now fails at the following lines:

DECLARE @dataType nvarchar(100)
DECLARE @statement nvarchar(250)

set @dataType = 
SELECT c.*, s.name 
FROM sys.columns c 
INNER JOIN sys.objects o 
ON c.object_id = o.object_id 
INNER JOIN sys.types s 
ON c.user_type_id = s.user_type_id 
WHERE o.name = 'a' AND c.name = 'test'
set @Statement = 'Alter table dbo.t_hist_Devicereport add test ' + @dataType 
exec (@Statement)

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The Error message is that I've incorrect syntax near SELECT but if I run the SELECT statement by itself it works quite fine... I'm using SQL Server 2005 in case that could be a problem

Answer 1

DECLARE @dataType nvarchar(100)
DECLARE @statement nvarchar(250)
SELECT @dataType = CASE WHEN s.name = 'nvarchar' THEN 'nvarchar(' + CAST(c.max_length AS varchar(4)) + ')' ELSE s.name END             
FROM sys.tables t JOIN sys.columns c ON t.object_id = c.object_id 
                  JOIN sys.types s ON c.user_type_id = s.user_type_id 
WHERE t.name = 'a' AND c.name = 'test'

SET @Statement = 'Alter table dbo.t_hist_Devicereport add test ' + @dataType 
EXEC sp_executesql @Statement