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 (
    21679, 21680, 21681, 21682, 21683, 21684, 
    21685, 21686, 21687, 21688, 21689, 
    21690, 21691, 21692, 21693, 21694
  ) 
  AND cscart_product_descriptions.lang_code = 'en'

Query time 0.00040

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 (21679,21680,21681,21682,21683,21684,21685,21686,21687,21688,21689,21690,21691,21692,21693,21694) and cscart_product_descriptions.lang_code = 'en'"
    }
  }
}

Result

product_id short_description full_description unit_name
21679 Tube-hydronic unit two front, left<p>Part number 58715T1000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21680 Connector Assembly - Brake Fluid Line<p>Part number 58723T1000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21681 connector<p>Part number 58724T4000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21682 Hose-brake front, left<p>Part number 58731T1600</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21683 Hose-brake front, right<p>Part number 58732T1600</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21684 Tube-connector to rear, left<p>Part number 58735T1000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21685 Tube-connector to rear, right<p>Part number 58736T1000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21686 Hose - Rear Wheel Left<p>Part number 58737T1200</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21687 Hose - Rear Brake Right<p>Part number 58738T1200</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21688 Clip<p>Part number 58751T4000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21689 Clip-Brake Fluid Line<p>Part number 58752D3400</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21690 Clip<p>Part number 58753J3000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21691 Clip-Brake Fluid Line<p>Part number 58756J3000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21692 Bracket-tube clip<p>Part number 58758T1000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21693 Sensor assembly - wheel speed, left<p>Part number 58930T1550</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21694 Sensor assembly - wheel speed, right<p>Part number 58940T1550</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>