Convert Many to one relation to one to one

[Digger]

I need compare two tables by text columns

Table1[MatchCol] has only unique text

Table2[MatchCol] has dublicates

I need found all MatchCol Ids from Table1 and Table2, to know which Ids from Table1[MatchCol] matches Table2[MatchCol] and wise versa (find difference in Tables)

one to one relations do this tricks but only with both tables unique values, and i got error "The cardinality you selected isnt valid for this relationship

How to do that? 

[PaulDBrown · Accepted solution]

Here is one way without changing the relationship:

Matching = 
COUNTROWS(
    INTERSECT(VALUES('Table 1'[T1]), VALUES('Table 2'[T2])))

No Match in T2 =
SUMX (
    VALUES ( 'Table 1'[T1] ),
    CALCULATE (
        IF (
            ISBLANK ( MAX ( 'Table 1'[T1] ) ),
            BLANK (),
            COUNTROWS ( EXCEPT ( VALUES ( 'Table 1'[T1] ), VALUES ( 'Table 2'[T2] ) ) )
        )
    )
)

No Match in T1 = 
COUNTROWS(EXCEPT(VALUES('Table 2'[T2]), VALUES('Table 1'[T1])))

[amitchandak]

@Digger , Best to keep one to many, unless there is an issue because of that