SELECT 
  cscart_product_prices.product_id, 
  MIN(
    IF(
      cscart_product_prices.percentage_discount = 0, 
      cscart_product_prices.price, 
      cscart_product_prices.price - (
        cscart_product_prices.price * cscart_product_prices.percentage_discount
      )/ 100
    )
  ) AS price 
FROM 
  cscart_product_prices 
WHERE 
  cscart_product_prices.product_id IN (
    6780, 6689, 6769, 6686, 6688, 6785, 6690, 
    6670, 6799, 6687, 6773, 6795, 6777, 
    6784, 6691, 6807, 6770, 6781, 6783, 
    6776, 6797, 6774, 6790, 7315, 6746, 
    6808, 6731, 6792, 6732, 6744, 6756, 
    6782, 6673, 6714, 6789, 6796, 6694, 
    6778, 6793, 6674, 6718, 6816, 6775, 
    6809, 6715, 6758, 6766, 6768, 6717, 
    6771, 6813, 6716, 6772, 6669, 6671, 
    6812, 6761, 6672, 6760, 6767, 6815, 
    6759, 6668, 6762, 6765, 6810, 6757, 
    6764, 6811, 6763, 6814
  ) 
  AND cscart_product_prices.lower_limit = 1 
  AND cscart_product_prices.usergroup_id IN (0, 1) 
GROUP BY 
  cscart_product_prices.product_id

Query time 0.00339

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "49.71"
    },
    "grouping_operation": {
      "using_filesort": false,
      "table": {
        "table_name": "cscart_product_prices",
        "access_type": "range",
        "possible_keys": [
          "usergroup",
          "product_id",
          "lower_limit",
          "usergroup_id"
        ],
        "key": "product_id",
        "used_key_parts": [
          "product_id"
        ],
        "key_length": "3",
        "rows_examined_per_scan": 71,
        "rows_produced_per_join": 14,
        "filtered": "19.99",
        "index_condition": "(`softwarepirmam_hewadelivard_cscart_4`.`cscart_product_prices`.`product_id` in (6780,6689,6769,6686,6688,6785,6690,6670,6799,6687,6773,6795,6777,6784,6691,6807,6770,6781,6783,6776,6797,6774,6790,7315,6746,6808,6731,6792,6732,6744,6756,6782,6673,6714,6789,6796,6694,6778,6793,6674,6718,6816,6775,6809,6715,6758,6766,6768,6717,6771,6813,6716,6772,6669,6671,6812,6761,6672,6760,6767,6815,6759,6668,6762,6765,6810,6757,6764,6811,6763,6814))",
        "cost_info": {
          "read_cost": "48.29",
          "eval_cost": "1.42",
          "prefix_cost": "49.71",
          "data_read_per_join": "340"
        },
        "used_columns": [
          "product_id",
          "price",
          "percentage_discount",
          "lower_limit",
          "usergroup_id"
        ],
        "attached_condition": "((`softwarepirmam_hewadelivard_cscart_4`.`cscart_product_prices`.`lower_limit` = 1) and (`softwarepirmam_hewadelivard_cscart_4`.`cscart_product_prices`.`usergroup_id` in (0,1)))"
      }
    }
  }
}