Wrong Data count of Left outer Join between 2 tables

Hi All,

I have created Calculation View and considered 2 tables inside projections and joined them with Left outer join.

Data count of Left side Table: 51731

Data count of right side table: 3760

Type of join: Left outer Join

There is a join (Left Outer join) condition between two tables based on Document Number.

But out put of join is not matching with data count of Left side table which is 51731. It is giving more records (64874) than actual (51731).

What would be the reason? 

What I should do to get correct count .

Are primary key combination should match between two tables?

Thanks in Advance.