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 (
    90150, 90165, 84073, 84081, 90149, 90164, 
    90142, 90157, 90148, 90163, 84072, 
    84080, 90147, 90162, 84071, 84079, 
    84095, 90141, 90156, 90297, 90304, 
    84057, 84065, 84070, 84078, 85973, 
    84069, 84077, 90140, 90155
  ) 
  AND cscart_product_descriptions.lang_code = 'en'

Query time 0.00072

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "13.52"
    },
    "table": {
      "table_name": "cscart_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": 30,
      "rows_produced_per_join": 30,
      "filtered": "100.00",
      "cost_info": {
        "read_cost": "10.52",
        "eval_cost": "3.00",
        "prefix_cost": "13.52",
        "data_read_per_join": "114K"
      },
      "used_columns": [
        "product_id",
        "lang_code",
        "short_description",
        "full_description"
      ],
      "attached_condition": "((`nuie_scalesta_net`.`cscart_product_descriptions`.`product_id` in (90150,90165,84073,84081,90149,90164,90142,90157,90148,90163,84072,84080,90147,90162,84071,84079,84095,90141,90156,90297,90304,84057,84065,84070,84078,85973,84069,84077,90140,90155)) and (`nuie_scalesta_net`.`cscart_product_descriptions`.`lang_code` = 'en'))"
    }
  }
}