SELECT 
  product_id, 
  group_id 
FROM 
  cscart_product_variation_group_products 
WHERE 
  group_id IN (
    623, 608, 642, 625, 547, 562, 622, 621, 
    552, 564, 673, 689, 555, 624, 667, 635, 
    679
  )

Query time 0.00121

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "48.36"
    },
    "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": 98,
      "rows_produced_per_join": 98,
      "filtered": "100.00",
      "index_condition": "(`softwarepirmam_hewadelivard_cscart_4`.`cscart_product_variation_group_products`.`group_id` in (623,608,642,625,547,562,622,621,552,564,673,689,555,624,667,635,679))",
      "cost_info": {
        "read_cost": "38.56",
        "eval_cost": "9.80",
        "prefix_cost": "48.36",
        "data_read_per_join": "1K"
      },
      "used_columns": [
        "product_id",
        "group_id"
      ]
    }
  }
}