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, 
  cscart_product_descriptions.unit_name 
FROM 
  cscart_product_descriptions 
WHERE 
  cscart_product_descriptions.product_id IN (
    21455, 21456, 21457, 21458, 21459, 21460, 
    21461, 21462, 21463, 21464, 21465, 
    21466, 21467, 21468, 21469, 21470
  ) 
  AND cscart_product_descriptions.lang_code = 'ru'

Query time 0.00057

JSON explain

{
  "query_block": {
    "select_id": 1,
    "table": {
      "table_name": "cscart_product_descriptions",
      "access_type": "range",
      "possible_keys": ["PRIMARY", "product_id", "idx_product_lang"],
      "key": "PRIMARY",
      "key_length": "9",
      "used_key_parts": ["product_id", "lang_code"],
      "rows": 16,
      "filtered": 100,
      "index_condition": "cscart_product_descriptions.product_id in (21455,21456,21457,21458,21459,21460,21461,21462,21463,21464,21465,21466,21467,21468,21469,21470) and cscart_product_descriptions.lang_code = 'ru'"
    }
  }
}

Result

product_id short_description full_description unit_name
21455 Cover-Heater<p>Part number 971A4T6050</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21456 Cover-Heater<p>Part number 971A5T6000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21457 Cover-Heater<p>Part number 971A5T6050</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21458 Thermistor Assembly-Air Conditioner Evaporator<p>Part number 97614T6000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21459 seal<p>Part number 971A6T6000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21460 COVER-DUST<p>Part number 97129T6000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21461 hose-drain<p>Part number 97173T6000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21462 seal<p>Part number 971A3T6040</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21463 Tapping screw - hexagon head<p>Part number 1244106167B</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21464 BRACKET<p>Part number 97556B8300</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21465 Duct Assembly - Air Intake<p>Part number 97190T6100</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21466 Case-left<p>Part number 971A7T6000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21467 Case-right<p>Part number 971A8T6000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21468 Sensor Assembly-Fine Dust<p>Part number 97253T6000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21469 control assembly<p>Part number 97255T6020</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21470 connector<p>Part number 97333T6500</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>