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 (
    21439, 21440, 21441, 21442, 21443, 21444, 
    21445, 21446, 21447, 21448, 21449, 
    21450, 21451, 21452, 21453, 21454
  ) 
  AND cscart_product_descriptions.lang_code = 'en'

Query time 0.00149

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 (21439,21440,21441,21442,21443,21444,21445,21446,21447,21448,21449,21450,21451,21452,21453,21454) and cscart_product_descriptions.lang_code = 'en'"
    }
  }
}

Result

product_id short_description full_description unit_name
21439 separator<p>Part number 97206T6000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21440 Door Assembly - Heater<p>Part number 97146T6550</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21441 door assy<p>Part number 971A1T6040</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21442 Arm-vent door<p>Part number 97224T6050</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21443 Arm-Flower Door<p>Part number 97185T6050</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21444 Arm-temp door, left<p>Part number 97186T6000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21445 Arm-temp door, right<p>Part number 97186T6050</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21446 Actuator - Temperature Door<p>Part number 97159T6000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21447 Actuator-Mode<p>Part number 97154T6050</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21448 Actuator - Temperature<p>Part number 97159C1150</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21449 Duct - shower, left<p>Part number 97279T6000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21450 Duct - shower, right<p>Part number 97282T6000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21451 heater core assembly<p>Part number 97138T6300</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21452 Evaporator Core Assembly<p>Part number 97139T6000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21453 seal<p>Part number 971A2T6000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21454 seal<p>Part number 971A2T6010</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>