I am trying convert a dictionary to simple comma separated string with duplicate keys removed.

here is my dictionary

"Message": [
        {
            "table_name": "sec_sp",
            "column_name": "field_1"
        },
        {
            "table_name": "sec_sp",
            "column_name": "field_2"
        },
        {
            "table_name": "sec_si",
            "column_name": "field_3"
        },
        {
            "table_name": "sec_si",
            "column_name": "field_4"
        },
        {
            "table_name": "sec_sp",
            "column_name": "field_5"
        },
    {
            "table_name": "sec_sc",
            "column_name": "field_6"
        },
    {
            "table_name": "sec_sc",
            "column_name": "field_7"
        }
    ]

I wanted to convert it to below strings.

sp_list = "field_1,field_2,field_5"
si_list = "field_3,field_4"
sc_list = "field_6,field_7"

I tried separating out to keys and values using below code however not able to remove dupes.

           for key, value in Message.items():