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 (
    5959, 41404, 33606, 2089, 3991, 6363, 
    15613, 40688, 1994, 3189, 350, 48849, 
    5643, 4823, 3186, 298, 37295, 4264, 
    4298, 1044, 1746, 351, 5457, 41112, 
    4272, 5472, 33464, 37298, 1850, 4814, 
    5588, 3992
  ) 
  AND cscart_product_descriptions.lang_code = 'en'

Query time 0.00370

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": 32,
          "filtered": 100,
          "index_condition": "cscart_product_descriptions.product_id in (5959,41404,33606,2089,3991,6363,15613,40688,1994,3189,350,48849,5643,4823,3186,298,37295,4264,4298,1044,1746,351,5457,41112,4272,5472,33464,37298,1850,4814,5588,3992) and cscart_product_descriptions.lang_code = 'en'"
        }
      }
    ]
  }
}