When you are creating relationships in PowerPivot you should see a number of tables and solid lines connecting them. If you have a dotted line (as shown below) it indicates an inactive relationship.
This could be purposefully done or else you have accidentally joined two tables together based on different fields e.g. the Date Field to the Date Field and the Time Field to the Date Field.
PowerPivot can only work on one relationship at a time so one will be active (solid line) and the others will be inactive (dotted line) between those tables.
If the wrong relationship is active, you can change it by right clicking on the line you want to be the active (solid) one and choose the ‘Mark as Active’ option.
If you made a mistake and want to remove one or more of them, right click on the ones you want to remove and click delete.
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