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Andy Leonard

Andy Leonard is an author and engineer who enjoys building and automating data integration solutions. Andy is co-host of the Data Driven podcast. Andy is no longer updating this blog. His current blog is

SSIS Snack: SSIS 2005 Lookup Transformations 101


I got ahead of myself in a post entitled SSIS Snack: Configuring an SSIS 2005 Lookup Transformation for a Left Outer Join and my friend Eric Wisdahl (Blog) called my out in the comments.

A Good Test

If you've not been warned previously, I'm an engineer. I learn an awful lot by testing - I sometimes refer to this as my poke-it-and-watch-where-it-wiggles methodology.

To test this, I created and populated two tables in my AndyWorks database, TestSourceA and TestLookupA, using the following T-SQL:

Use AndyWorks

Create Table TestSourceA
(ID int identity(1,1)
,name varchar(50))

Create Table TestLookupA
(ID int
,name varchar(50)
,value int)

insert into dbo.TestSourceA
select 'a'
union all
select 'b'
union all
select 'c'
union all
select 'd'

insert into dbo.TestLookupA
(name, value)
select 'a',11
union all
select 'a',22
union all
select 'b',33
union all
select 'b',44

Next, I tested a left join between the tables with this statement: 

select, b.value
from dbo.TestSourceA a
left join dbo.TestLookupA b
 on =

The results are:


In an SSIS Data Flow Task, I added an OLE DB Source Adapter and set it to read from AndyWorks using a SQL Statement:

Select name
From dbo.TestSourceA

Downstream, I connected a Lookup Transformation aimed at AndyWorks.dbo.TestLookupA. On the Columns tab the Lookup auto-mapped the name fields. I selected the value field from the Available Lookup Columns:

I clicked the Configure Error Output button and set the Lookup Error response to "Ignore failure":

I closed the Lookup Transformation editor and added a Trash Destination Adapter from I also added a Grid Data Viewer between the Lookup and Trash Destination, so when comepleted the Data Flow Task appeared as shown:

When I execute the package, the data viewer displays the results predicted in Eric's comment:

As Eric pointed out, the Lookup still only returns the first match in the table. There are results missing from the Left Join statement results shown earlier.

But the Lookup does not fail when there is no match - it simply returns NULL as the Left Join does. That was the point I was trying to make in the earlier post, but I didn't do a very good job. Thanks for pointing that out Eric!

:{> Andy

Published Tuesday, February 16, 2010 8:00 AM by andyleonard
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Jonathan Amen said:

Thanks for this bit. The way the outbound success link reads it won't pass records with no match even if 'Ignore Failure' is selected. Thanks for saving me the testing time to figure this out on my own. /Thumbs up!

October 12, 2010 4:05 PM

Mohamed Harris said:

Good post

September 29, 2011 4:52 AM

Kamakshi Suram said:

Its really useful. Merge Join will take Sorted input and performs Left/swapleft(right)/full/inner joins where as Lookup will do left join.

June 15, 2012 5:30 AM

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