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 (
    20525, 20526, 20527, 20528, 20529, 20530, 
    20531, 20532, 20533, 20534, 20535, 
    20536, 20537, 20538, 20539, 20540
  ) 
  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 (20525,20526,20527,20528,20529,20530,20531,20532,20533,20534,20535,20536,20537,20538,20539,20540) and cscart_product_descriptions.lang_code = 'en'"
    }
  }
}

Result

product_id short_description full_description unit_name
20525 Trim assembly - rear transverse<p>Part number 85770T6500UBL</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
20526 Switch assembly - seat back remote folding<p>Part number 894B0T6110</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
20527 Socket Assembly-Accessories<p>Part number 95120C7000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
20528 Bezel assembly rear air vent right side<p>Part number 97980T6000NNB</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
20529 Bezel assembly rear air vent left<p>Part number 97990T6000NNB</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
20530 Trim Assembly - Front Pillar<p>Part number 85810T6500DUE</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
20531 Trim assembly - front pillar, right<p>Part number 85820T6500DUE</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
20532 Trim Assembly - Cowl Side Left<p>Part number 85823T6000UBL</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
20533 Trim Assembly - Cowl Side Right<p>Part number 85824T6000UBL</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
20534 Trim assembly - center pillar upper, left<p>Part number 85830T6500DUE</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
20535 Trim assembly - center pillar upper, right<p>Part number 85840T6500DUE</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
20536 Knob-Height Adjust, Left<p>Part number 85834T6000DUE</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
20537 Cover assembly-height adjust, left<p>Part number 85833T6000DUE</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
20538 Knob-Height Adjust, Right<p>Part number 85844T6000DUE</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
20539 Trim assembly - center pillar lower, left<p>Part number 85835T6500UBL</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
20540 Cover assembly-height adjust, right<p>Part number 85843T6000DUE</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>