Using ATTR function

We have to use ATTR function when creating a calculated using 2 dates from 2 different Databases.

1) If we create a calculated field using two dates are from same Databases , no need to use "ATTR" function as prefix.

2) If both dates are from 2 different bases (Data Blending) then must have to use ""ATTR" function as prefix.

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And when have to add the both Date fields in the Report to get the Final Result.

Note: We have to define the Relationship of two Dates in two Databases then we don't nulls in the Report.