If I understand that medium post correctly it’s just a left join, so in DataFrames:
julia> using DataFrames
julia> df_1 = DataFrame(id = [1002, 1004, 1006],
first_name = ["Cersei", "Daenerys", "Arya"])
3×2 DataFrame
Row │ id first_name
│ Int64 String
─────┼───────────────────
1 │ 1002 Cersei
2 │ 1004 Daenerys
3 │ 1006 Arya
julia> df_2 = DataFrame(id = [1003, 1004, 1005, 1002, 1006],
last_name = ["Tyrell", "Targaryen", "Snow", "Lannister", "Stark"])
5×2 DataFrame
Row │ id last_name
│ Int64 String
─────┼──────────────────
1 │ 1003 Tyrell
2 │ 1004 Targaryen
3 │ 1005 Snow
4 │ 1002 Lannister
5 │ 1006 Stark
julia> leftjoin(df_1, df_2, on = :id)
3×3 DataFrame
Row │ id first_name last_name
│ Int64 String String?
─────┼──────────────────────────────
1 │ 1004 Daenerys Targaryen
2 │ 1002 Cersei Lannister
3 │ 1006 Arya Stark