SELECT 
  prices.product_id, 
  prices.lower_limit, 
  usergroup_id, 
  prices.percentage_discount, 
  IF(
    prices.percentage_discount = 0, 
    prices.price, 
    prices.price - (
      prices.price * prices.percentage_discount
    )/ 100
  ) as price 
FROM 
  cscart_product_prices prices 
WHERE 
  prices.product_id = 167412 
  AND lower_limit > 1 
  AND prices.usergroup_id IN (0, 0, 1) 
ORDER BY 
  lower_limit

Query time 0.00037

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost": 0.00194677,
    "nested_loop": [
      {
        "table": {
          "table_name": "prices",
          "access_type": "range",
          "possible_keys": [
            "usergroup",
            "product_id",
            "lower_limit",
            "usergroup_id",
            "wdbi_product_id_lower_limit_usergroup_id_price_eff1727beeef",
            "wdbi_usergroup_id_lower_limit_product_id_92b7e8f6a250",
            "wdbi_product_id_lower_limit_usergroup_id_price_perc_3b2301d551d0",
            "wdbi_lower_limit_usergroup_id_product_id_b93629431718"
          ],
          "key": "wdbi_product_id_lower_limit_usergroup_id_price_perc_3b2301d551d0",
          "key_length": "6",
          "used_key_parts": ["product_id", "lower_limit"],
          "loops": 1,
          "rows": 1,
          "cost": 0.00194677,
          "filtered": 0.003359173,
          "attached_condition": "prices.product_id <=> 167412 and prices.lower_limit > 1 and prices.usergroup_id in (0,0,1)",
          "using_index": true
        }
      }
    ]
  }
}