SSIS Package not wanting to fetch metadata of temporary table

Using WITH RESULT SETS to explicitly define the metadata will allow SSIS to skip the sp_describe_first_result_set step and use the metadata that you define. The upside is that you can use this to get SSIS to execute SQL that contains a temporary table (for me, that performance helped a lot); the downside is, you have to manually maintain and update this if anything changes.

Query sample (stored procedure:)

    EXEC ('dbo.MyStoredProcedure')
    WITH RESULT SETS
      (
        (
            MyIntegerColumn INT NOT NULL,
            MyTextColumn VARCHAR(50) NULL,
            MyOtherColumn BIT NULL
        )
      )

Query sample (simple SQL:)

EXEC ('
    CREATE TABLE #a 
      (
        MyIntegerColumn INT NOT NULL,
        MyTextColumn VARCHAR(50) NULL,
        MyOtherColumn BIT NULL
      ) 
    INSERT INTO #a 
      (
        MyIntegerColumn,
        MyTextColumn,
        MyOtherColumn
      )
    SELECT 
        1 AS MyIntegerColumn,
        ''x'' AS MyTextColumn,
        0 AS MyOtherColumn

    SELECT MyIntegerColumn, MyTextColumn, MyOtherColumn
    FROM #a')

WITH RESULT SETS
    (
        (
            MyIntegerColumn INT NOT NULL
           ,MyTextColumn VARCHAR(50) NULL
           ,MyOtherColumn BIT NULL
        )
    )

If you are working on SSIS 2012, then it uses system stored procedure sp_describe_first_result_set to fetch the metadata of the tables and it does not support temporary tables. But you can go for other options like table variables and CTEs which are going to work fine. https://connect.microsoft.com/SQLServer/feedback/details/629077/denali-engine-metadata-discovery-shuns-temp-tables

Another option (kind of a hack, but it works and doesn't require you to change your use of global temp tables) is to use a SET FMTONLY ON command in front of your actual query to send a fake "First result set" to SSIS with your correct column structure. So you can do something like

SET FMTONLY ON
select 0 as a, 1 as b, 'test' as C, GETDATE() as D
SET FMTONLY OFF

select a, b, c, d from ##TempTable

When SSIS runs sp_describe_first_result_set, it will return the metadata and column names of your FMTONLY command, and won't complain about not being able to determine the metadata of your temp table because it won't even try.

I had faced a similar issue when SSSI packages were migrated from 2008 to 2016. The latest version uses sp_describe_first_result_set to fetch metadata and it does not work with temporary tables. As a workaround, I used the below query in the OLEDB source editor. I did not change the SQL stored procedure, and it still uses a temporary table. Do be sure to use the Parse Query and Preview option to ensure it works fine. See the image below.

Query:

EXEC [dbo].[spGetNames]
WITH RESULT SETS((
        FirstName varchar(50), 
        LastName varchar(50)
));