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Community Team Member
Community Team Member
For general information on types of data relationships, potential complications and how to resolve them, see the following articles: 
The Invisible Many to Many
You may find instances where you have common symptoms of a many to many (M2M) relationship, but cannot find the root cause of the relationship. Such symptoms of a many to many relationship include:
  • High RAM usage during query,
  • ElastiCube size on disk increasing during query,
  • Build failing with 100% RAM
The common check for a M2M is the below query.
Select count(, distinct_count( From dim as a
However, the numbers may be identical which may not initially indicate a M2M so the below query must be run for a stronger check:
Select count(a.ID), distinct_count(a.ID), 
sum(case when a.ID is null then 1 else 0 end) as [null count]
From dim as a
If the null count field shows more than 1 in both tables then you have a many-to-many relationship on null values.
There could be many reasons why null values get to the dimension tables, such as cases when the dimension table is a custom table that's taken from the fact table or if the data is imported with null values from the data source itself.
Proactive Solutions
  • Dimension tables should always be unique, even if they have null values, there shouldn't be more than one null value.
  • If the dimension table is a custom table that's taken from the fact table, make sure you use the "distinct" expression.
  • If the nulls are imported from the data source try to remove them either in the import query or by creating a custom table that's taking only unique values from the table.
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Last update:
‎02-21-2024 11:26 AM
Updated by:
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