SELECT 
  q_product_descriptions.product_id, 
  q_product_descriptions.short_description, 
  IF(
    q_product_descriptions.short_description = '', 
    q_product_descriptions.full_description, 
    ''
  ) AS full_description 
FROM 
  q_product_descriptions 
WHERE 
  q_product_descriptions.product_id IN (46652, 46651, 46650) 
  AND q_product_descriptions.lang_code = 'en'

Query time 0.00034

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "7.21"
    },
    "table": {
      "table_name": "q_product_descriptions",
      "access_type": "range",
      "possible_keys": [
        "PRIMARY",
        "product_id"
      ],
      "key": "PRIMARY",
      "used_key_parts": [
        "product_id",
        "lang_code"
      ],
      "key_length": "9",
      "rows_examined_per_scan": 3,
      "rows_produced_per_join": 3,
      "filtered": "100.00",
      "index_condition": "((`portal`.`q_product_descriptions`.`product_id` in (46652,46651,46650)) and (`portal`.`q_product_descriptions`.`lang_code` = 'en'))",
      "cost_info": {
        "read_cost": "6.61",
        "eval_cost": "0.60",
        "prefix_cost": "7.21",
        "data_read_per_join": "11K"
      },
      "used_columns": [
        "product_id",
        "lang_code",
        "short_description",
        "full_description"
      ]
    }
  }
}

Result

product_id short_description full_description
46650 <p>A very strong coffee, tasteful and aromatic, with an high percentage of Asian and African Robusta perfectly mixed with Brazilian and Indian Arabica. For those who love a creamy and intense espresso coffee</p>
46651 <p>This is the blend for those who love the typical Italian espresso. It is created from the select combination of Arabica beans grown in the plateaus of Brazil and the prized Robusta beans from India, Africa and the Far East</p>
46652 <p>An excellent decaffeinated coffee. It retains all the flavour and aroma of classic coffee thanks to the careful selection of varieties and the special roasting procedure. As required by Italian regulations, this blend may not contain more than 0,1 % of caffeine per cup</p>