SELECT 
  cscart_products.* 
FROM 
  cscart_products 
WHERE 
  cscart_products.product_id IN (
    1242, 1241, 1240, 1239, 1238, 1237, 1236, 
    1235, 1234, 1233, 1232, 1231
  )

Query time 0.00092

JSON explain

{
  "query_block": {
    "select_id": 1,
    "table": {
      "table_name": "cscart_products",
      "access_type": "range",
      "possible_keys": ["PRIMARY"],
      "key": "PRIMARY",
      "key_length": "3",
      "used_key_parts": ["product_id"],
      "rows": 12,
      "filtered": 100,
      "index_condition": "cscart_products.product_id in (1242,1241,1240,1239,1238,1237,1236,1235,1234,1233,1232,1231)"
    }
  }
}