SELECT 
  p.product_id, 
  p.list_price, 
  pp.price, 
  ROUND(
    (p.list_price - pp.price) / p.list_price * 100
  ) AS discount_pct 
FROM 
  cscart_products p 
  INNER JOIN cscart_product_prices pp ON pp.product_id = p.product_id 
  AND pp.lower_limit = 1 
WHERE 
  p.product_id IN (
    461025, 461181, 111833, 312414, 461219, 
    390978, 11893, 312412, 312456, 461036, 
    153, 312443, 230, 312444, 391037, 312436, 
    461212, 312847, 312450, 168, 312451, 
    391029, 390993, 164, 312418, 391030, 
    12708, 227, 221, 233, 116547, 461189, 
    461276, 312458, 119, 312455, 170, 21914, 
    165, 312424, 391040, 312724, 312419, 
    22384, 391025, 312446, 393787, 461033, 
    312870, 116427, 202, 11677, 183, 400913, 
    312863, 312411, 312864, 312421, 312051, 
    461190, 312449, 111, 166, 312723, 116539, 
    461035, 400924, 9, 461034, 461027, 
    312856, 116529, 312849, 280, 312043, 
    312416, 400914, 312466, 187, 116425
  ) 
  AND p.status = 'A' 
  AND p.list_price > 0 
  AND p.list_price > pp.price 
  AND ROUND(
    (p.list_price - pp.price) / p.list_price * 100
  ) >= 5

Query time 0.00135

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost": 0.28259592,
    "nested_loop": [
      {
        "table": {
          "table_name": "p",
          "access_type": "range",
          "possible_keys": ["PRIMARY", "status"],
          "key": "PRIMARY",
          "key_length": "3",
          "used_key_parts": ["product_id"],
          "loops": 1,
          "rows": 80,
          "cost": 0.13989432,
          "filtered": 100,
          "attached_condition": "p.product_id in (461025,461181,111833,312414,461219,390978,11893,312412,312456,461036,153,312443,230,312444,391037,312436,461212,312847,312450,168,312451,391029,390993,164,312418,391030,12708,227,221,233,116547,461189,461276,312458,119,312455,170,21914,165,312424,391040,312724,312419,22384,391025,312446,393787,461033,312870,116427,202,11677,183,400913,312863,312411,312864,312421,312051,461190,312449,111,166,312723,116539,461035,400924,9,461034,461027,312856,116529,312849,280,312043,312416,400914,312466,187,116425) and p.`status` = 'A' and p.list_price > 0"
        }
      },
      {
        "table": {
          "table_name": "pp",
          "access_type": "ref",
          "possible_keys": ["usergroup", "product_id", "lower_limit"],
          "key": "usergroup",
          "key_length": "3",
          "used_key_parts": ["product_id"],
          "ref": ["u985510652_ecartify.p.product_id"],
          "loops": 80,
          "rows": 1,
          "cost": 0.1427016,
          "filtered": 100,
          "attached_condition": "pp.lower_limit = 1 and p.list_price > pp.price and round((p.list_price - pp.price) / p.list_price * 100,0) >= 5"
        }
      }
    ]
  }
}