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 (
    6859, 7420, 6474, 6602, 7082, 7225, 7379, 
    6941, 6485, 7121, 6803, 6502, 7380, 
    6862, 6676, 6857, 6498, 6885, 7086, 
    6537, 6876, 7028, 7714, 7040, 7176, 
    6546, 7020, 7043, 6464, 6483, 6938, 
    7168, 6609, 7260, 7375, 7033, 6481, 
    8041, 7186, 6463, 6466, 6911, 7576, 
    6877, 6800, 6994, 7032, 7084, 7414, 
    7236, 6882, 6500, 6868, 6993, 8150, 
    6734, 6497, 6539, 6720, 6787, 7195, 
    7325, 6480, 6991, 7023, 7036, 7323, 
    7951, 6504, 6564, 6858, 7027, 7049, 
    7085, 7175, 7321, 7400, 7441, 7025, 
    6467
  ) 
  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 0.00206

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "56.01"
    },
    "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": 80,
        "rows_produced_per_join": 15,
        "filtered": "19.99",
        "index_condition": "(`softwarepirmam_hewadelivard_cscart_4`.`cscart_product_prices`.`product_id` in (6859,7420,6474,6602,7082,7225,7379,6941,6485,7121,6803,6502,7380,6862,6676,6857,6498,6885,7086,6537,6876,7028,7714,7040,7176,6546,7020,7043,6464,6483,6938,7168,6609,7260,7375,7033,6481,8041,7186,6463,6466,6911,7576,6877,6800,6994,7032,7084,7414,7236,6882,6500,6868,6993,8150,6734,6497,6539,6720,6787,7195,7325,6480,6991,7023,7036,7323,7951,6504,6564,6858,7027,7049,7085,7175,7321,7400,7441,7025,6467))",
        "cost_info": {
          "read_cost": "54.41",
          "eval_cost": "1.60",
          "prefix_cost": "56.01",
          "data_read_per_join": "383"
        },
        "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)))"
      }
    }
  }
}