Table Merge creates duplicate records

[DataGuy2016]

Hi Folks,

I am stumped.

I am trying to merge two tables into a new table using a LEFT JOIN.  Both tables have unique records on each row.  When I join the tables, BI creates duplicate rows on some records for no apparent reason.  The duplicates are identical in every way.

Can anybody explain this?  Is this a bug?

[J_R_Cribb]

Hi @DataGuy2016, 

If you haven't already found a solution...

I had a similar issue where LEFT JOIN was creating duplicates, resulting over 1000 rows of data where I should have just 85.

I solved the issue by expanding the relative columns as an aggregate, instead of just an expansion.

Hope that this makes sense.

[Anonymous]

I am having the same problem with my data.  And no, I do not understand your answer to "expand as an aggregate," will you please clarify?

I know this is an old thread, but if someone else is still reading this thread and would like to offer help, I appreciate it!

[Anonymous]

HI JR,

Thank you for the response.  Could you send me an email at trossgreene@stormsmart.com.  I want to talk with you more and share a sample file, but I can't figure out how to upload an excel file here.

Thanks,

Tera

[J_R_Cribb]

Hi @Anonymous, 

I have created a quick sample that I hope helps explain my method. It may not work with your data, but it did fix the issue with mine!

I have two tables, I would like to merge 'Customer Type' with 'Customer Name'.

Customer Name Table

Customer Type Table

I would like to merge using the 'ID' column in both, to bring in the 'Cust Type' field from table 'Customer Type' into table 'Customer Name'.

 Merge Options

Once successfully merged, I see the below:

 I now have the option to expand that column of the merged table to bring in data from the 'Customer Type' table. But this is where I choose to Aggregate a field rather than expand. You may require a different aggregate measure other than median, dependant on data type:

Expand as Aggregate

The result from my data is below:

Result

Please also see sample.pbix file which I hope can help you with your issue.

[DataGuy2016]

Hi,

The LEFT JOIN table Merge is creating duplicate records from the LHS table. 

I understand what a LEFT JOIN is. 

My LHS table only has unique rows.  Why is PowerBI creating duplicate records?  These are 100% identical in every respect.

SQL JOINS