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 (
    3866, 3867, 3868, 3869, 3865, 3870, 3872, 
    3871, 3876, 3862, 3863, 35730, 3864, 
    3861, 35731, 3873, 47984, 3874, 3884, 
    3875, 3880, 3877, 3859, 3879, 35729, 
    3881, 3860, 3883, 3882, 35859
  ) 
  AND cscart_product_descriptions.lang_code = 'en'

Query time 0.00136

JSON explain

{
  "query_block": {
    "select_id": 1,
    "nested_loop": [
      {
        "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": 30,
          "filtered": 100,
          "index_condition": "cscart_product_descriptions.product_id in (3866,3867,3868,3869,3865,3870,3872,3871,3876,3862,3863,35730,3864,3861,35731,3873,47984,3874,3884,3875,3880,3877,3859,3879,35729,3881,3860,3883,3882,35859) and cscart_product_descriptions.lang_code = 'en'"
        }
      }
    ]
  }
}