What does Extend Merge Dimensions mean?

To understand the extend merge dimensions option it would be beneficial first of all to understand what a merged dimension is.

A merged dimension is simply a join between two or more queries contained within a single Webi report therefore allowing us to use data in the same block from multiple queries.
What type of Join is used depends on which objects you choose to display in your block.

For example

  • If I were to choose the Merged ID object and an object from each query then a Full Outer Join would be produced. Meaning that all records from each query would be returned.
  • If I were to choose one of the ID’s from one query and then another object from each query then a Left or Right Outer Join would be produced and only show values pertaining to the query with which the ID was chosen from.
  • NB: If I were to choose two unmerged objects that foreseeably should be merged and attempted to display the data in the block I would receive a Data Synch error.

Now to answer the question at hand “What does it mean to extend a Merged Dimension?”

Accessed from within the document properties window it is a checkbox that is not selected by default. This option, however, will only work when unmerged dimensions are not selected in the block.

Extending the merged dimension essentially turns what would otherwise be a Left or Right Outer Join into a Full Outer Join.
Meaning that all records regardless of an exact match between the merged fields have data for the unmerged data.


Extend Merged Dimensions (EMD) effects how a business objects document handles the join between multiple data providers. Depending on how you join and display objects from each data provider.

The main thing to remember is that Extend Merge Dimensions will only have an impact when using the non-merged dimension.

for example:
MD – this is your merged dimension
MD1 – Object from query 1
MD2 – Object from query 2

When displaying the result block using:
MD – Extend Merge Dimension will have no impact
MD1 – Without EMD the result set will show as a left join between query 1 and query 2
MD2 – Without EMD the result set will show as a right join between query 1 and query 2

However, when selecting EMD using MD1 or MD2 in your result set will result in effectively a Full other join as will be seen when using MD in your result set.

So why not just use MD in your result set and not worry about EMD? There may be any number of reasons why you may need to display MD1 or MD2.

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