SELECT 
  q_product_prices.product_id, 
  MIN(
    IF(
      q_product_prices.percentage_discount = 0, 
      q_product_prices.price, 
      q_product_prices.price - (
        q_product_prices.price * q_product_prices.percentage_discount
      )/ 100
    )
  ) AS price 
FROM 
  q_product_prices 
WHERE 
  q_product_prices.product_id IN (
    8395, 8396, 8397, 8398, 8399, 8400, 8401, 
    8402, 8403, 8404, 8405, 8406, 8407, 
    8408, 8409, 8410, 8412, 8414, 8415, 
    8419, 8425, 8426, 8427, 8428, 8429, 
    8430, 8431, 8432, 8435, 8436, 8438, 
    8439
  ) 
  AND q_product_prices.lower_limit = 1 
  AND q_product_prices.usergroup_id IN (0, 1) 
GROUP BY 
  q_product_prices.product_id

Query time 0.00134

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "78.21"
    },
    "grouping_operation": {
      "using_filesort": false,
      "table": {
        "table_name": "q_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": 33,
        "rows_produced_per_join": 6,
        "filtered": "19.99",
        "index_condition": "(`portal`.`q_product_prices`.`product_id` in (8395,8396,8397,8398,8399,8400,8401,8402,8403,8404,8405,8406,8407,8408,8409,8410,8412,8414,8415,8419,8425,8426,8427,8428,8429,8430,8431,8432,8435,8436,8438,8439))",
        "cost_info": {
          "read_cost": "76.89",
          "eval_cost": "1.32",
          "prefix_cost": "78.21",
          "data_read_per_join": "158"
        },
        "used_columns": [
          "product_id",
          "price",
          "percentage_discount",
          "lower_limit",
          "usergroup_id"
        ],
        "attached_condition": "((`portal`.`q_product_prices`.`lower_limit` = 1) and (`portal`.`q_product_prices`.`usergroup_id` in (0,1)))"
      }
    }
  }
}