SELECT 
  cscart_vendor_following.user_id, 
  followed_on, 
  firstname, 
  lastname, 
  email 
FROM 
  cscart_vendor_following 
  LEFT JOIN cscart_users ON cscart_users.user_id = cscart_vendor_following.user_id 
WHERE 
  cscart_vendor_following.vendor_id = 193 
ORDER BY 
  followed_on desc

Query time 0.00071

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "17.80"
    },
    "ordering_operation": {
      "using_filesort": true,
      "cost_info": {
        "sort_cost": "7.30"
      },
      "nested_loop": [
        {
          "table": {
            "table_name": "cscart_vendor_following",
            "access_type": "ALL",
            "rows_examined_per_scan": 73,
            "rows_produced_per_join": 7,
            "filtered": "10.00",
            "cost_info": {
              "read_cost": "7.22",
              "eval_cost": "0.73",
              "prefix_cost": "7.95",
              "data_read_per_join": "233"
            },
            "used_columns": [
              "user_id",
              "vendor_id",
              "followed_on"
            ],
            "attached_condition": "(`cscartdb`.`cscart_vendor_following`.`vendor_id` = 193)"
          }
        },
        {
          "table": {
            "table_name": "cscart_users",
            "access_type": "eq_ref",
            "possible_keys": [
              "PRIMARY"
            ],
            "key": "PRIMARY",
            "used_key_parts": [
              "user_id"
            ],
            "key_length": "3",
            "ref": [
              "cscartdb.cscart_vendor_following.user_id"
            ],
            "rows_examined_per_scan": 1,
            "rows_produced_per_join": 7,
            "filtered": "100.00",
            "cost_info": {
              "read_cost": "1.83",
              "eval_cost": "0.73",
              "prefix_cost": "10.50",
              "data_read_per_join": "48K"
            },
            "used_columns": [
              "user_id",
              "firstname",
              "lastname",
              "email"
            ],
            "attached_condition": "<if>(is_not_null_compl(cscart_users), (`cscartdb`.`cscart_users`.`user_id` = `cscartdb`.`cscart_vendor_following`.`user_id`), true)"
          }
        }
      ]
    }
  }
}