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 (
    21375, 21376, 21377, 21378, 21379, 21380, 
    21381, 21382, 21383, 21384, 21385, 
    21386, 21387, 21388, 21389, 21390
  ) 
  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 (21375,21376,21377,21378,21379,21380,21381,21382,21383,21384,21385,21386,21387,21388,21389,21390) and cscart_product_descriptions.lang_code = 'en'"
    }
  }
}

Result

product_id short_description full_description unit_name
21375 Speaker assembly - subwoofer, left<p>Part number 96380T6500UBL</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21376 Speaker assembly - subwoofer, right<p>Part number 96380T6550UBL</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21377 Sensor assembly - active road noise control<p>Part number 96398T6700</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21378 Bracket-set mounting, left<p>Part number 96175T6000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21379 Bracket-set mounting, right<p>Part number 96176T6000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21380 Cable Assembly-USB<p>Part number 96595T6000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21381 Head Unit Assembly - AVN<p>Part number 96560T6000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21382 Monitor Assembly-Front AVN<p>Part number 96525T60004X</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21383 Horn Assembly - Low Pitch<p>Part number 96611T6000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21384 Horn Assembly - High Pitch<p>Part number 96621T6000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21385 Motor & Link Assembly - Windshield Wipers<p>Part number 98100T6000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21386 Arm assembly - windshield wiper (driver's side)<p>Part number 98311T6000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21387 Arm assembly - windshield wiper (passenger seat)<p>Part number 98321T6000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21388 Rail spring-wiper blade, passenger seat<p>Part number 98365S9000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21389 Rubber assembly - wiper blade (passenger seat)<p>Part number 983612V000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21390 Blade assembly - wiper, passenger seat<p>Part number 98360S9000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>