String concatenation in SQL doesn't work - sql

Question

I am wondering why the following doesn't work:
INSERT INTO #Data2 (FileName,Field)
SELECT #FileName as FileName, * FROM OPENROWSET(BULK '\\serverpath\' + #FileName , SINGLE_CLOB) AS Contents
I tried also the second approach but with this one I get the error message that the variable isn't declared:
declare #path nvarchar(255) = 'SELECT #FileName as FileName, * FROM OPENROWSET(BULK ''\\serverpath\' + #FileName + ''', SINGLE_CLOB) AS Contents'
INSERT INTO #Data2 (FileName,Field)
EXEC(#path)
Can somebody help?
Thanks

Answer 1

You can not pass #FileName as FileName using exec, but you can using sp_executesql -- but you still can not pass #FileName as part of openrowset():
declare #path nvarchar(4000) = N'
select #FileName as FileName, *
from openrowset(bulk ''\\serverpath\' + #FileName + '''
, single_clob) as Contents'
insert into #Data2 (FileName,Field)
exec sp_executesql, N'#FileName nvarchar(1024))',#FileName
Or directly concatenating it like you are for the bulk source:
declare #path nvarchar(4000) = N'
select '+quotename(#FileName,'''')+' as FileName, *
from openrowset(bulk '+quotename('\\serverpath\'+#FileName,'''')+'
, single_clob) as Contents'
insert into #Data2 (FileName,Field)
exec sp_executesql #path
reference:
The curse and blessings of dynamic SQL - Erland Sommarskog
sp_executesql

Answer 2

You cannot use OPENROWSET with a variable path. Check this:
--This works
DECLARE #Data2 TABLE(Field VARBINARY(MAX));
INSERT INTO #Data2 (Field)
SELECT * FROM OPENROWSET(BULK 'F:\Privat\StackOverflow\test.xml' , SINGLE_BLOB) AS Contents;
SELECT CAST(Field AS NVARCHAR(MAX)) FROM #Data2;
--This breaks at syntax check
DECLARE #FileName AS VARCHAR(1000)='F:\Privat\StackOverflow\test.xml';
INSERT INTO #Data2 (Field)
SELECT * FROM OPENROWSET(BULK #FileName , SINGLE_BLOB) AS Contents;
SELECT CAST(Field AS NVARCHAR(MAX)) FROM #Data2;
--This works, but needs a physically created table. Your table variable is out of scope within the EXEC-execution
CREATE TABLE Data2(Field VARBINARY(MAX));
DECLARE #FileName AS VARCHAR(1000)='F:\Privat\StackOverflow\test.xml';
DECLARE #cmd VARCHAR(MAX)='INSERT INTO Data2(Field) SELECT * FROM OPENROWSET(BULK ''' + #FileName + ''', SINGLE_BLOB) AS Contents;'
EXEC(#cmd);
SELECT * FROM Data2;
GO
DROP TABLE Data2;
Instead of the physically created table you might use an output parameter.