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 (
    1157, 1180, 394, 910, 1158, 1449, 2096, 
    2505, 502, 1137, 323, 516, 791, 1064, 
    1177, 1245, 1256, 915, 921, 924, 1246, 
    1357, 518, 994, 997, 1113, 1203, 1369, 
    1390, 2504, 321, 361
  ) 
  AND cscart_product_descriptions.lang_code = 'en'

Query time 0.00093

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 (1157,1180,394,910,1158,1449,2096,2505,502,1137,323,516,791,1064,1177,1245,1256,915,921,924,1246,1357,518,994,997,1113,1203,1369,1390,2504,321,361) and cscart_product_descriptions.lang_code = 'en'"
    }
  }
}

Result

product_id short_description full_description
321
323
361
394
502
516
518
791
910
915
921
924
994
997
1064
1113
1137
1157
1158
1177
1180
1203
1245 <p>Test</p>
1246 <p>Test</p>
1256 <p>Test dungeon</p>
1357
1369
1390
1449 <p>test boost</p>
2096
2504 <p>test time cart</p>
2505 <p>test time cart</p>