hadoop - Find common elements using Pig script -

i newbie world of hadoop,currently exploring pig scripts. have write pig scripts finds out common data between 2 files.

for instanace,

samplefilea has data:

1,a,,m

2,b,25,f

the above data describes column 1 id, column 2 name,column 3 age , column 4 gender

samplefileb has same data:

1,a,,m

2,b,25,f

i tried various joins not getting expected output because of blank or null present in column 3 of first record.

the expected output is:

(2,b,25,f),(2,b,25,f) (1,a,,m),(1,a,,m)

but getting is:

(2,b,25,f),(2,b,25,f), ,(1,a,,m)

i not sure empty data coming in output.

your highly appreciated.