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 (
    20589, 20590, 20591, 20592, 20593, 20594, 
    20595, 20596, 20597, 20598, 20599, 
    20600, 20601, 20602, 20603, 20604
  ) 
  AND cscart_product_descriptions.lang_code = 'ru'

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 (20589,20590,20591,20592,20593,20594,20595,20596,20597,20598,20599,20600,20601,20602,20603,20604) and cscart_product_descriptions.lang_code = 'ru'"
    }
  }
}

Result

product_id short_description full_description unit_name
20589 Glass assembly - front door, left<p>Part number 82410T1010</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
20590 Glass assembly - front door, right<p>Part number 82420T1010</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
20591 Glass front door fixed, left<p>Part number 82570T1010</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
20592 Fixed glass front door, right<p>Part number 82580T1010</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
20593 Panel assembly - front door module, left<p>Part number 82471T1000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
20594 Panel assembly - front door module, right<p>Part number 82481T1000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
20595 Retainer - front door latch, left<p>Part number 82472T1000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
20596 Adapter-door latch, left<p>Part number 82486T1000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
20597 Retainer - Front Door Latch Right<p>Part number 82482T1000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
20598 Adapter-door latch, right<p>Part number 82496T1000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
20599 Channel assembly - front door lower, left<p>Part number 82550T1000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
20600 Channel assembly - front door lower, right<p>Part number 82560T1000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
20601 Antenna Assembly-Smart Key<p>Part number 95460L1200</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
20602 Weatherstrip assembly-rear door side<p>Part number 83130T1000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
20603 Weather strip-rear door parting, left<p>Part number 831A0T1000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
20604 Weather strip-rear door parting, right<p>Part number 831B0T1000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>