investigating additional rows added after running a left join on two tables

[haider_imam]

How do you guys investigate where these additional rows came from? 

I tried adding a variable in one of the data sets before doing the left join 

data original_tbl_1; set table1;

testvar = 1;

run; 

then in the following step I do the left join

I thought I could just find where 1 doesn't exist after I run the left join, but it turns out all the addition rows are also filled out with testvar =1  

😞 

Any advice on how I can go about doing this? 

[tomrvincent]

'the left join'...to what table? From what table? By what fields? No idea what the other table involved looks like...maybe it already has a testvar field in it.

Or, if you're left joining original_tbl_1 to some other table by some field(s) it isn't surprising the results would have testvar =1.