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 (
    20477, 20478, 20479, 20480, 20481, 20482, 
    20483, 20484, 20485, 20486, 20487, 
    20488, 20489, 20490, 20491, 20492
  ) 
  AND cscart_product_descriptions.lang_code = 'en'

Query time 0.00089

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 (20477,20478,20479,20480,20481,20482,20483,20484,20485,20486,20487,20488,20489,20490,20491,20492) and cscart_product_descriptions.lang_code = 'en'"
    }
  }
}

Result

product_id short_description full_description unit_name
20477 Control Assembly - Heater<p>Part number 97250T6300RET</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
20478 Control assembly - rear heater<p>Part number 97950T6110RET</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
20479 Bolt-Washer Assembly<p>Part number 84433T6000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
20480 Bar Assembly - Cowl Cross<p>Part number 84410T6100</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
20481 bolt washer assembly<p>Part number 84434T6000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
20482 glove box assembly<p>Part number 84510T6000DUE</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
20483 Housing Assembly - Glove Box<p>Part number 84540T6000NNB</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
20484 Pin-glove box damper<p>Part number 84522D2000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
20485 Crash pad assembly-main<p>Part number 84710T6300UBL</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
20486 Panel assembly - center fascia, upper part<p>Part number 84835T6000UBL</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
20487 Pad-Crash Pad Main<p>Part number 84714T1000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
20488 Grille Assembly - Center Speaker<p>Part number 84715T6000UBL</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
20489 Panel assembly - lower crash pad, left<p>Part number 84750T6000DUE</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
20490 Panel Assembly-Lower Crash Pad<p>Part number 84730T6100DUE</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
20491 Panel Assembly - Lower Center<p>Part number 84735T6000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
20492 Panel assembly - lower crash pad, right<p>Part number 84734T6100DUE</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>