SELECT 
  cscart_product_descriptions.product_id, 
  cscart_product_descriptions.short_description, 
  IF(
    cscart_product_descriptions.short_description = '' 
    OR cscart_product_descriptions.short_description IS NULL, 
    cscart_product_descriptions.full_description, 
    ''
  ) AS full_description 
FROM 
  cscart_product_descriptions 
WHERE 
  cscart_product_descriptions.product_id IN (
    704, 717, 1046, 1050, 1060, 1181, 1194, 
    1361, 1396, 2412, 3012, 333, 344, 655, 
    689, 743, 990, 1062, 1096, 1207, 1208, 
    1395, 1399, 1820, 1826, 2115, 2178, 
    2332, 2506, 336, 408, 456
  ) 
  AND cscart_product_descriptions.lang_code = 'en'

Query time 0.00118

JSON explain

{
  "query_block": {
    "select_id": 1,
    "table": {
      "table_name": "cscart_product_descriptions",
      "access_type": "range",
      "possible_keys": ["PRIMARY", "product_id"],
      "key": "PRIMARY",
      "key_length": "11",
      "used_key_parts": ["product_id", "lang_code"],
      "rows": 32,
      "filtered": 100,
      "index_condition": "cscart_product_descriptions.product_id in (704,717,1046,1050,1060,1181,1194,1361,1396,2412,3012,333,344,655,689,743,990,1062,1096,1207,1208,1395,1399,1820,1826,2115,2178,2332,2506,336,408,456) and cscart_product_descriptions.lang_code = 'en'"
    }
  }
}

Result

product_id short_description full_description
333
336
344
408
456
655
689
704
717
743
990
1046
1050
1060
1062
1096
1181
1194
1207
1208
1361
1395
1396
1399
1820
1826
2115
2178
2332
2412
2506
3012