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 (
    20509, 20510, 20511, 20512, 20513, 20514, 
    20515, 20516, 20517, 20518, 20519, 
    20520, 20521, 20522, 20523, 20524
  ) 
  AND cscart_product_descriptions.lang_code = 'en'

Query time 0.00043

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 (20509,20510,20511,20512,20513,20514,20515,20516,20517,20518,20519,20520,20521,20522,20523,20524) and cscart_product_descriptions.lang_code = 'en'"
    }
  }
}

Result

product_id short_description full_description unit_name
20509 Vanity Mirror Assy-Rear<p>Part number 85385T6550DUE</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
20510 Plug-trim mounting<p>Part number 857463L000DUE</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
20511 Wiring assembly - loop<p>Part number 91801T6471</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
20512 Microphone assembly - active road noise control<p>Part number 96578T6700DUE</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
20513 Trim assembly - luggage side, left<p>Part number 85730T6630UBL</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
20514 Cover-luggage side trim, left<p>Part number 85735T6000UBL</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
20515 Cover-luggage side right<p>Part number 85748T6500UBL</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
20516 Trim assembly - luggage side, right<p>Part number 85740T6600UBL</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
20517 Tray assembly-luggage side right<p>Part number 85747T6500UBL</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
20518 Handle Assembly - Luggage Floor Box<p>Part number 85729T6000UBL</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
20519 Tray-Side Cover<p>Part number 857E9T6000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
20520 Tray Assembly-Luggage<p>Part number 85757T6500UBL</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
20521 Tray assembly-luggage side, left<p>Part number 85737T6500UBL</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
20522 Case Assembly-Cap<p>Part number 857B2T6000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
20523 Tray Cover-Battery<p>Part number 857C5T6500UBL</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
20524 Clip-spring trim mounting<p>Part number 846473S000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>