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 (
    20573, 20574, 20575, 20576, 20577, 20578, 
    20579, 20580, 20581, 20582, 20583, 
    20584, 20585, 20586, 20587, 20588
  ) 
  AND cscart_product_descriptions.lang_code = 'en'

Query time 0.00035

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 (20573,20574,20575,20576,20577,20578,20579,20580,20581,20582,20583,20584,20585,20586,20587,20588) and cscart_product_descriptions.lang_code = 'en'"
    }
  }
}

Result

product_id short_description full_description unit_name
20573 Cab-front door pull handle, left<p>Part number 82714T1000NBD</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
20574 Cab-front door pull handle, right<p>Part number 82724T1000NBD</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
20575 Cover-outer side mirror, left<p>Part number 87607T1000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
20576 Cover-outer side mirror, right<p>Part number 87608T1000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
20577 Lamp assembly - front door foot, left<p>Part number 92630T1000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
20578 Lamp assembly - front door foot, right<p>Part number 92640T1000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
20579 Switch Assembly - IMS Control<p>Part number 93250T1000VCS</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
20580 Speaker assembly - tweeter, left<p>Part number 96310T1500</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
20581 Speaker assembly - tweeter, right<p>Part number 96311T1500</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
20582 Speaker assembly - midrange, left<p>Part number 96320T1500</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
20583 Latch assembly - front door, left<p>Part number 81310T1410</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
20584 Latch sub assembly - front door, left<p>Part number 81301T1110</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
20585 Latch assembly - front door, right<p>Part number 81320T1420</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
20586 Latch sub assembly - front door, right<p>Part number 81302T1120</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
20587 Connection cage-door inside handle, left<p>Part number 81316T1000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
20588 Connection cage - door inside handle, right<p>Part number 81326T1000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>