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 (
    6415, 6416, 6417, 6418, 6419, 6420, 6421, 
    6422, 6423, 6424, 6425, 6426, 6427, 
    6428, 6429, 6430, 6431, 6432, 6433, 
    6434, 6435, 6436, 6437, 6438, 6439, 
    6440, 6441, 6442, 6443, 6444, 6445, 
    6446, 6447, 6448, 6449, 6450, 6451, 
    6452, 6453, 6454, 6456, 6457, 6458, 
    6459, 6460, 6461, 6462, 6463, 6464, 
    6465, 6466, 6467, 6468, 6469, 6470, 
    6471, 6472, 6473, 6474, 6475, 6476, 
    6477, 6478, 6479
  ) 
  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 0.00154

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "153.61"
    },
    "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": 64,
        "rows_produced_per_join": 12,
        "filtered": "19.99",
        "index_condition": "(`portal`.`q_product_prices`.`product_id` in (6415,6416,6417,6418,6419,6420,6421,6422,6423,6424,6425,6426,6427,6428,6429,6430,6431,6432,6433,6434,6435,6436,6437,6438,6439,6440,6441,6442,6443,6444,6445,6446,6447,6448,6449,6450,6451,6452,6453,6454,6456,6457,6458,6459,6460,6461,6462,6463,6464,6465,6466,6467,6468,6469,6470,6471,6472,6473,6474,6475,6476,6477,6478,6479))",
        "cost_info": {
          "read_cost": "151.05",
          "eval_cost": "2.56",
          "prefix_cost": "153.61",
          "data_read_per_join": "307"
        },
        "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)))"
      }
    }
  }
}