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SELECT 
  product_id, 
  group_id 
FROM 
  cscart_product_variation_group_products 
WHERE 
  group_id IN (90, 89, 92, 88, 91, 94)

Query time 0.00045

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "32.61"
    },
    "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": 19,
      "rows_produced_per_join": 19,
      "filtered": "100.00",
      "index_condition": "(`cscart`.`cscart_product_variation_group_products`.`group_id` in (90,89,92,88,91,94))",
      "cost_info": {
        "read_cost": "28.81",
        "eval_cost": "3.80",
        "prefix_cost": "32.61",
        "data_read_per_join": "304"
      },
      "used_columns": [
        "product_id",
        "group_id"
      ]
    }
  }
}

Result

product_id	group_id
853	88
852	88
858	89
857	89
856	89
855	89
854	89
863	90
862	90
861	90
860	90
859	90
867	91
866	91
865	91
864	91
872	92
871	92
870	92
869	92
868	92
878	94
877	94
876	94
875	94

product_id	group_id
853	88
852	88
858	89
857	89
856	89
855	89
854	89
863	90
862	90
861	90
860	90
859	90
867	91
866	91
865	91
864	91
872	92
871	92
870	92
869	92
868	92
878	94
877	94
876	94
875	94

product_id	group_id
853	88
852	88
858	89
857	89
856	89
855	89
854	89
863	90
862	90
861	90
860	90
859	90
867	91
866	91
865	91
864	91
872	92
871	92
870	92
869	92
868	92
878	94
877	94
876	94
875	94

product_id	group_id
853	88
852	88
858	89
857	89
856	89
855	89
854	89
863	90
862	90
861	90
860	90
859	90
867	91
866	91
865	91
864	91
872	92
871	92
870	92
869	92
868	92
878	94
877	94
876	94
875	94