SELECT 
  product_id, 
  group_id 
FROM 
  cscart_product_variation_group_products 
WHERE 
  group_id IN (
    598, 597, 589, 600, 594, 596, 595, 599, 
    591, 603, 593, 592, 601, 602, 686, 678, 
    618, 680
  )

Query time 0.00066

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "22.06"
    },
    "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": 39,
      "rows_produced_per_join": 39,
      "filtered": "100.00",
      "index_condition": "(`softwarepirmam_hewadelivard_cscart_4`.`cscart_product_variation_group_products`.`group_id` in (598,597,589,600,594,596,595,599,591,603,593,592,601,602,686,678,618,680))",
      "cost_info": {
        "read_cost": "18.16",
        "eval_cost": "3.90",
        "prefix_cost": "22.06",
        "data_read_per_join": "624"
      },
      "used_columns": [
        "product_id",
        "group_id"
      ]
    }
  }
}