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Mike ArthurMike Arthur 

Help Text on Roll-Up Summary

I came across this in the help text for Roll-Up Summary Fields (

User-added image

What does it mean?

RUSs can only be created on master-detail relationships, not lookups.
I set up a lookup field with 'Don't allow deletion...' option on a detail object and created a RUS on the master but the the lookup on the detail wasn't available as a count.

It sounds like an important point but I can't get how it is applied.

Anyone know?

Mike ArthurMike Arthur
Maybe it controls the ability to create a RUS on a formula field on the detail object where the formula field includes a lookup, but only if 'Don't allow deletion...' is selected on lookup definition.  However, I tried setting this up in DE and didn't get the formula field available to sum.