SELECT 
  req_prod.required_id 
FROM 
  cscart_product_required_products as req_prod 
  LEFT JOIN cscart_products ON req_prod.required_id = cscart_products.product_id 
WHERE 
  req_prod.product_id = 339678 
  AND cscart_products.status != 'D' 
GROUP BY 
  req_prod.required_id

Query time 0.00081

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "2.40"
    },
    "grouping_operation": {
      "using_filesort": false,
      "nested_loop": [
        {
          "table": {
            "table_name": "req_prod",
            "access_type": "ref",
            "possible_keys": [
              "PRIMARY"
            ],
            "key": "PRIMARY",
            "used_key_parts": [
              "product_id"
            ],
            "key_length": "3",
            "ref": [
              "const"
            ],
            "rows_examined_per_scan": 1,
            "rows_produced_per_join": 1,
            "filtered": "100.00",
            "using_index": true,
            "cost_info": {
              "read_cost": "1.00",
              "eval_cost": "0.20",
              "prefix_cost": "1.20",
              "data_read_per_join": "8"
            },
            "used_columns": [
              "product_id",
              "required_id"
            ],
            "attached_condition": "((`webmarco`.`req_prod`.`product_id` <=> 339678))"
          }
        },
        {
          "table": {
            "table_name": "cscart_products",
            "access_type": "eq_ref",
            "possible_keys": [
              "PRIMARY",
              "status"
            ],
            "key": "PRIMARY",
            "used_key_parts": [
              "product_id"
            ],
            "key_length": "3",
            "ref": [
              "webmarco.req_prod.required_id"
            ],
            "rows_examined_per_scan": 1,
            "rows_produced_per_join": 0,
            "filtered": "50.79",
            "cost_info": {
              "read_cost": "1.00",
              "eval_cost": "0.10",
              "prefix_cost": "2.40",
              "data_read_per_join": "3K"
            },
            "used_columns": [
              "product_id",
              "status"
            ],
            "attached_condition": "(`webmarco`.`cscart_products`.`status` <> 'D')"
          }
        }
      ]
    }
  }
}