Create Relationship on Compound Key

[raeldor]

So, can someone tell me why I can't join tables on more than one key?  This seems like one of the most basic query functions yet it can't be done.  I see people saying 'create a calculated column', but how is that efficient?  Now the whole think becomes text and I likely need to pad the ID fields too to avoid incorrect keys.

[Anonymous]

You can do it in M. If you choose in your transformation in Home/ "Merge Queries", you can highlight the 2 columns to match in both sides of the join.

[Anonymous]

@Anonymous what next? I merged the tables using 3 columns "Merge Queries" and "Merge Queries as New". With the first option it appears as a new column labled "Table", but I can't figure out how to add this data to the dashboard. When using "Merge Queries as New", a new table is created, but a) It doesn't have all columns, and b) the tables don't seem to be linked.

My expectation is that when I select a row in the "Parent" table visual, the "Child table" is filtered with just those rows.

Ex: 

Parent
A-1-x
A-1-y
A-1-z

Child
A-1-x-1

A-1-x-2
A-1-y-1

A-1-y-2
A-1-z-1

A-1-z-2

When I select a row in "Parent", "Child" only shows two rows.

[Anonymous]

Hi sorry only seeing this now - just expand the column (seems your are only clicking the record) and you should see everything (check the type of join too, by default left outer join)

[v-xjiin-msft]

@raeldor

In current Power BI, there exists a limitation for relationship that you can’t create relationship based on more than one column. 

To workaround this limitation, we can concatenate these related columns into one calculated column, then create relationship based on this concatenate column. Please refer:

Reference: Relationship in Power BI with Multiple Columns 

Thanks,
Xi Jin.

[raeldor]

So, I know HOW to do it.  The question is really... why do I need to?

[v-xjiin-msft]

@raeldor

This is the limitation for relationship in current Power BI and it is by design.

Thanks,
Xi Jin.

[raeldor]

A little odd considering every relational database I've ever seen allows multi-field joins.  Seems a little unfair making users jump through hoops to do something so common. 😞

[databass]

I agree. it's crazy that 6 years after this original post you still can't create a table relationship on multiple keys 😂