6 Replies Latest reply on Nov 16, 2018 6:33 AM by Michael Gillespie

    Linking more fields for data Blending

    jon rios

      i see alot of linking icons on my secondary data source..... only 2 in "active", (red icon).  i have some calculation that use fields from secondary source and i feel i am not gettng the proper results. i am troubleshooting and cant see why.... I am left with potential blending issues, i have over 20 relationships Tableau has  automatically detected.  I am linking based on 2 fields....

       

      Does linking more fields between primary and secondary have any effect on filtering or calculations?  should adding links be decided on fields used in calculations?

        • 1. Re: Linking more fields for data Blending
          Chris McClellan

          Most definitely.  You can link as many fields as you need to for the calculations to work properly - that might be 1 field or many it just depends on your data.

          • 2. Re: Linking more fields for data Blending
            Michael Gillespie

            That is a very open-ended question, Jon.  There is no single answer to it.  What you do to blend data sources is completely dependent on the results you are trying to achieve.

             

            When creating a blend, Tableau automatically matches based on the column name.  If you have lots of matching column names between 2 data sources, Tableau will create a link for every match it finds.  That is rarely (never?) the right thing to do.  Usually, I get rid of ALL the automatic links and create only the ones I need.

             

            Without seeing your data and without understanding precisely what you think is incorrect about the current data, it's not possible to be more specific.

            • 3. Re: Linking more fields for data Blending
              jon rios

              what determines why you would add more linking fields...

               

              "if your calculations uses fields from secondary data source you must link the field"  is there any rhyme or reason?

               

              my data is linked by fields in filter shelf.... why link to other fields, what drives that decision?

              • 4. Re: Linking more fields for data Blending
                Michael Gillespie

                Now we're getting into relational theory! 

                 

                If you have 2 independent data sources, you can DISPLAY data from one data source at a time, and you can't put data from the OTHER data source on the same worksheet as the FIRST data source, because there is no connection between the 2 sets of data.

                 

                We link (BLEND) 2 data sources so that we can put data from BOTH data sources in the same worksheet.  Often, it's something as simple as getting the SUM() of Invoice Amount from one data source, for each customer (from a different data source).  All we need to do that is to link on ONE field shared between the two data sources (in this case, perhaps that's Customer Number).

                 

                In cases where there are a LOT of common fields between data sources, it's up to YOU to determine what the logical connection between the data sources should be, for the result you are trying to obtain.  Again, it is VERY hard to give you any specific advice here, because we don't know what your data looks like.

                 

                "if your calculations uses fields from secondary data source you must link the field"  is there any rhyme or reason? - YES, there is.  It is critical to get your Blend fields set up correctly or you WILL get bad results.  But exactly what you need to blend on is completely dependent on what your data looks like and what you're trying to do.

                 

                my data is linked by fields in filter shelf.... why link to other fields, what drives that decision?  I don't know what that means, Jon.  Do you mean you put a field in the Filter shelf that also has a Link icon next to it in the Dimensions or Measures pane?

                • 5. Re: Linking more fields for data Blending
                  jon rios

                  very nice of you go to in details Mike.

                   

                  your right, trying to troubleshoot a specific problem based on my data is difficult, ill continue to do my own research and see what i can find for my specific situation.  thanks for the try

                  • 6. Re: Linking more fields for data Blending
                    Michael Gillespie

                    Happy to try, at least!

                     

                    Good luck, and keep asking questions.