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 (
    133812, 138080, 133813, 133814, 138365, 
    138079
  ) 
  AND product_descriptions.lang_code = 'en'

Query time 0.00842

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "5.02"
    },
    "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": 6,
      "rows_produced_per_join": 6,
      "filtered": "100.00",
      "cost_info": {
        "read_cost": "4.42",
        "eval_cost": "0.60",
        "prefix_cost": "5.02",
        "data_read_per_join": "30K"
      },
      "used_columns": [
        "product_id",
        "lang_code",
        "short_description",
        "full_description"
      ],
      "attached_condition": "((`goimagine`.`product_descriptions`.`product_id` in (133812,138080,133813,133814,138365,138079)) and (`goimagine`.`product_descriptions`.`lang_code` = 'en'))"
    }
  }
}