int is incompatible with uniqueidentifier when no int usage - sql

Question

I am getting this error when there is absolutely no usage of int anywhere.
I have this stored procedure
ALTER procedure [dbo].[usp_GetFileGuid] #fileType varchar(25)
as
select [id] from fileTypes where dirId = #fileType
Here id is a uniqueidentifier in fileTypes table
When I execute the following
declare #fileGuid uniqueidentifier
exec #fileGuid = usp_GetFileGuid 'accounts'
print #fileGuid
I get the following error
(1 row(s) affected)
Msg 206, Level 16, State 2, Procedure usp_GetFileGuid, Line 0
Operand type clash: int is incompatible with uniqueidentifier
Is there anything wrong with the syntax of assigning output of stored procedure to the local variable? Thank you.

Answer 1

You are using EXEC #fileGuid = procedure syntax which is used for retrieving return values, not resultsets. Return values are restricted to INT and should only be used to return status / error codes, not data.
What you want to do is use an OUTPUT parameter:
ALTER procedure [dbo].[usp_GetFileGuid]
#fileType varchar(25),
#id UNIQUEIDENTIFIER OUTPUT
AS
BEGIN
SET NOCOUNT ON;
SELECT #id = [id] from dbo.fileTypes where dirId = #fileType;
-- if the procedure *also* needs to return this as a resultset:
SELECT [id] = #id;
END
GO
Then for usage:
declare #fileGuid uniqueidentifier;
exec dbo.usp_GetFileGuid #fileType = 'accounts', #id = #fileGuid OUTPUT;
print #fileGuid;

Answer 2

create procedure [dbo].[usp_GetFileGuid] #fileType varchar(25),#uuid uniqueidentifier output
as
select #uuid=[id] from fileTypes where dirId = #fileType
declare #fileGuid uniqueidentifier
exec usp_GetFileGuid 'accounts',#fileGuid output
print #fileGuid

Answer 3

The value returned is an int as it is the status of the execution
From CREATE PROCEDURE (Transact-SQL)
Return a status value to a calling procedure or batch to indicate
success or failure (and the reason for failure).
You are looking for an output parameter.
OUT | OUTPUT
Indicates that the parameter is an output parameter. Use
OUTPUT parameters to return values to the caller of the procedure.
text, ntext, and image parameters cannot be used as OUTPUT parameters,
unless the procedure is a CLR procedure. An output parameter can be a
cursor placeholder, unless the procedure is a CLR procedure. A
table-value data type cannot be specified as an OUTPUT parameter of a
procedure.