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SELECT 
  product_id, 
  group_id 
FROM 
  cscart_product_variation_group_products 
WHERE 
  group_id IN (115, 57, 58, 55, 56)

Query time 0.00035

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "35.81"
    },
    "table": {
      "table_name": "cscart_product_variation_group_products",
      "access_type": "range",
      "possible_keys": [
        "idx_group_id"
      ],
      "key": "idx_group_id",
      "used_key_parts": [
        "group_id"
      ],
      "key_length": "3",
      "rows_examined_per_scan": 22,
      "rows_produced_per_join": 22,
      "filtered": "100.00",
      "index_condition": "(`cscart`.`cscart_product_variation_group_products`.`group_id` in (115,57,58,55,56))",
      "cost_info": {
        "read_cost": "31.41",
        "eval_cost": "4.40",
        "prefix_cost": "35.81",
        "data_read_per_join": "352"
      },
      "used_columns": [
        "product_id",
        "group_id"
      ]
    }
  }
}

Result

product_id	group_id
704	55
703	55
663	55
710	55
709	55
708	55
707	55
706	55
719	56
718	56
717	56
716	56
715	56
714	56
713	56
711	56
666	56
724	57
723	57
722	57
721	57
720	57
726	58
725	58
727	58
956	115
957	115
958	115

product_id	group_id
704	55
703	55
663	55
710	55
709	55
708	55
707	55
706	55
719	56
718	56
717	56
716	56
715	56
714	56
713	56
711	56
666	56
724	57
723	57
722	57
721	57
720	57
726	58
725	58
727	58
956	115
957	115
958	115

product_id	group_id
704	55
703	55
663	55
710	55
709	55
708	55
707	55
706	55
719	56
718	56
717	56
716	56
715	56
714	56
713	56
711	56
666	56
724	57
723	57
722	57
721	57
720	57
726	58
725	58
727	58
956	115
957	115
958	115

product_id	group_id
704	55
703	55
663	55
710	55
709	55
708	55
707	55
706	55
719	56
718	56
717	56
716	56
715	56
714	56
713	56
711	56
666	56
724	57
723	57
722	57
721	57
720	57
726	58
725	58
727	58
956	115
957	115
958	115