table A table B table C

hsa-miR-100-5p 1.8 hsa-miR-100 1.0 hsa-mir-100 0 1.0

hsa-miR-101-3p 0.7 hsa-mir-100-5p 2.5 hsa-miR-100-5p 1.8 2.5

hsa-miR-101-5p 2.4 hsa-mir-101-5p 2 hsa-miR-101-3p 0.7 0

                                                                                                        hsa-mir-101-5p 2.4  2

i have two csv files like A n B, how can i get a file C(merge of A n B)?? if values is not present in any of the file it should be consider as zero.. i tried with join function it gives the file but zero values is not mentioned