Merging two asymmetrical tables

Okay, so after much bang of my head against a DAX shaped brick wall, and using the helpful suggestions by lbendlin I have managed to get closer to what I was looking for.  In the end I used the followign approach:

I defined two tables using SUMMARIZE and SELECTCOLUMNS, then using NATURALLEFTOUTERJOIN to join them together.  One thing to note was, data lineage meant that my join kept failing.  I got around this by appending a 0 to the key value being used to join tables - this broke the lineage and allowed the join to work.  I've included the code below in case it helps people to understand the approach.

var tableA = SELECTCOLUMNS(SUMMARIZE(sprint,
                                     sprint[squad_sprint],
                                     sprint[sprint_id],
                                     sprint[name]),
                          "squad_sprint", [squad_sprint]&"0",
                          "sprint_id", [sprint_id],
                          [name])

var tableB = SELECTCOLUMNS(SUMMARIZE(history_sprint_summary,
                                     history_sprint_summary[squad_sprint],
                                     history_sprint_summary[project_key],
                                     history_sprint_summary[max_sprint_date]),
                       "squad_sprint", [squad_sprint]&"0",
                       "project_key", [project_key],
                       "max_sprint_date",[max_sprint_date])
var result = NATURALLEFTOUTERJOIN(tableB, tableA)
RETURN result