Without seeing your data It'll be difficult for us to give you any solution. Try to share some mock up data in .twbx format.
Don't know how much this will help but you can try something like this. Create a calc field using below logic
COUNTD([Your Customer ID Field])>1
Drag this field to filters shelf and select only "False". It will exclude duplicate customers.
What is the name of the field taht has the duplicate value.
And how do you know that it is duplicate ?
All fields are same for both records
If u copy & paste data in excel & check dupes it will show you.
You need to work with your data source. Don't know which data source you're using. This is not the right solution but as you've mentioned you don't want to use custom sql. Don't know why? You can try something like this. Put extract filter like this.
This solution only works for your given data set. Don't know will it be work for your original data or not?
If you're using excel then select all the rows and columns then remove duplicate
If you're using some db source like oracle, my sql etc then first of all try to put some check constraints so that you can reduce the redundancy of your data. Try to add some additional date & time identifier so that you can identify the load time of your data. If its duplicate record then you can see the date time of duplicate records. Coming to your original scenario Create a view of your distinct records then connect to tableau.
Some useful link.
Let us know If you've any question.
Many thanks. I did it in custom sql & works well.
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