SELECT 
  product_descriptions.product_id, 
  product_descriptions.short_description, 
  IF(
    product_descriptions.short_description = '' 
    OR product_descriptions.short_description IS NULL, 
    product_descriptions.full_description, 
    ''
  ) AS full_description 
FROM 
  product_descriptions 
WHERE 
  product_descriptions.product_id IN (
    399709, 399715, 399753, 400280, 401024, 
    401025, 401035, 401067, 401081, 401616, 
    401622, 401634, 402338, 402353, 402902, 
    402933, 402938, 403680, 403692, 403709, 
    404244, 404249, 404267, 404982
  ) 
  AND product_descriptions.lang_code = 'en'

Query time 0.00124

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "19.76"
    },
    "table": {
      "table_name": "product_descriptions",
      "access_type": "range",
      "possible_keys": [
        "PRIMARY",
        "product_id"
      ],
      "key": "PRIMARY",
      "used_key_parts": [
        "product_id",
        "lang_code"
      ],
      "key_length": "11",
      "rows_examined_per_scan": 24,
      "rows_produced_per_join": 24,
      "filtered": "100.00",
      "cost_info": {
        "read_cost": "17.36",
        "eval_cost": "2.40",
        "prefix_cost": "19.76",
        "data_read_per_join": "122K"
      },
      "used_columns": [
        "product_id",
        "lang_code",
        "short_description",
        "full_description"
      ],
      "attached_condition": "((`goimagine`.`product_descriptions`.`product_id` in (399709,399715,399753,400280,401024,401025,401035,401067,401081,401616,401622,401634,402338,402353,402902,402933,402938,403680,403692,403709,404244,404249,404267,404982)) and (`goimagine`.`product_descriptions`.`lang_code` = 'en'))"
    }
  }
}