Code:
$ cat mac_discount.txt
1030064,8959,1,12380005080811105527,Customer
620500,1238,1,12380005080811102840,Customer
620528,1238,1,12380005080811142338,Customer
620535,1238,1,12380005080811142752,Customer
620543,1238,1,12380005080811144409,Customer
620545,1238,1,12380005080811144809,Customer
634952,1238,1,12380005080811102548,Customer
TransDiscountGroupTransactionID,TransDiscountGroupStoreID,SequenceID,AlternateCustomerID,DiscountGroupID
[pkdprd1@test-dwbi-app2:/import/volsap/dev]
$ cat mac_trans.txt
StoreCENTER,625_1030061_830 AM,3485e17a-0baa-46a9-9edf-07a0858c4188,1030061,8956,1,625,MBROWNE,3,000000011603
StoreCENTER,625_1030062_833 AM,992b6947-a404-4e10-8e35-44dd85ccd5ee,1030062,8957,1,625,MBROWNE,3,000000011603
StoreCENTER,625_1030063_838 AM,aa742016-0b68-4155-bc60-ca44f3dd504b,1030063,8958,1,625,MBROWNE,3,000000011603
StoreCENTER,625_1030064_839 AM,898189a4-7e5e-4341-9492-d6b72549c9bc,1030064,8959,1,625,MBROWNE,3,000000011603
StoreCENTER,625_1030065_841 AM,01fc6fa4-6f40-47ce-ab76-fad4ddd88d6b,1030065,8960,1,625,MBROWNE,3,000000011603
StoreCENTER,625_1030066_843 AM,6ddef2a7-8e11-4076-91fa-8cf3a1d8e3e0,1030066,8961,1,625,MBROWNE,3,000000011603
StoreCENTER,625_1030067_844 AM,7d7ae219-70b7-4b8e-a282-a5a3a4cb2074,1030067,8962,1,625,MBROWNE,3,000000011603
[pkdprd1@test-dwbi-app2:/import/volsap/dev]
$ nawk -F, '
NR == FNR { a[$1","$2]="," $3 "," $4 "," $5 }
NR != FNR && $4","$5 in a { print $0 "," a[$4","$5]}
NR != FNR && !($4","$5 in a) { print $0 ",,,," }
' mac_discount.txt mac_trans.txt
StoreCENTER,625_1030061_830 AM,3485e17a-0baa-46a9-9edf-07a0858c4188,1030061,8956,1,625,MBROWNE,3,000000011603,,,,
StoreCENTER,625_1030062_833 AM,992b6947-a404-4e10-8e35-44dd85ccd5ee,1030062,8957,1,625,MBROWNE,3,000000011603,,,,
StoreCENTER,625_1030063_838 AM,aa742016-0b68-4155-bc60-ca44f3dd504b,1030063,8958,1,625,MBROWNE,3,000000011603,,,,
StoreCENTER,625_1030064_839 AM,898189a4-7e5e-4341-9492-d6b72549c9bc,1030064,8959,1,625,MBROWNE,3,000000011603,,1,12380005080811105527,Customer
StoreCENTER,625_1030065_841 AM,01fc6fa4-6f40-47ce-ab76-fad4ddd88d6b,1030065,8960,1,625,MBROWNE,3,000000011603,,,,
StoreCENTER,625_1030066_843 AM,6ddef2a7-8e11-4076-91fa-8cf3a1d8e3e0,1030066,8961,1,625,MBROWNE,3,000000011603,,,,
StoreCENTER,625_1030067_844 AM,7d7ae219-70b7-4b8e-a282-a5a3a4cb2074,1030067,8962,1,625,MBROWNE,3,000000011603,,,,