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 (
    47655, 27359, 34555, 31638, 33312, 31633, 
    5300, 5991, 5297, 1980, 31634, 31639, 
    3570, 3569, 31636, 1979, 1088, 17259, 
    398, 1981, 31637, 5278, 31635, 1580, 
    48980, 120, 37850, 1538, 48558, 15322, 
    6274, 40381
  ) 
  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 0.01374

JSON explain

{
  "query_block": {
    "select_id": 1,
    "nested_loop": [
      {
        "table": {
          "table_name": "cscart_product_prices",
          "access_type": "range",
          "possible_keys": [
            "usergroup",
            "product_id",
            "lower_limit",
            "usergroup_id"
          ],
          "key": "product_id",
          "key_length": "3",
          "used_key_parts": ["product_id"],
          "rows": 32,
          "filtered": 99.9960556,
          "index_condition": "cscart_product_prices.product_id in (47655,27359,34555,31638,33312,31633,5300,5991,5297,1980,31634,31639,3570,3569,31636,1979,1088,17259,398,1981,31637,5278,31635,1580,48980,120,37850,1538,48558,15322,6274,40381)",
          "attached_condition": "cscart_product_prices.lower_limit = 1 and cscart_product_prices.usergroup_id in (0,1)"
        }
      }
    ]
  }
}