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 (
    21085, 21086, 21087, 21088, 21089, 21090, 
    21091, 21092, 21093, 21094, 21095, 
    21096, 21097, 21098, 21099, 21100
  ) 
  AND cscart_product_descriptions.lang_code = 'ru'

Query time 0.00031

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 (21085,21086,21087,21088,21089,21090,21091,21092,21093,21094,21095,21096,21097,21098,21099,21100) and cscart_product_descriptions.lang_code = 'ru'"
    }
  }
}

Result

product_id short_description full_description unit_name
21085 End piece - air duct, right<p>Part number 86546T6000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21086 Tapping screws - bumper mounting<p>Part number 865793K000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21087 Clip<p>Part number 8659324000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21088 Cover - active air sealing, left<p>Part number 86971T6000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21089 Cover - active air sealing, right<p>Part number 86972T6000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21090 Wiring Harness - Front Bumper<p>Part number 91890T6030</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21091 Unit Assembly - Front View Camera<p>Part number 99250T6000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21092 Bracket-license plate mounting<p>Part number 69157T6000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21093 Cover - Rear Bumper Lower<p>Part number 86612T6000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21094 Bracket - rear bumper side mounting, left<p>Part number 86651T6000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21095 Bracket-rear beam upper mounting<p>Part number 86633T6000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21096 Bracket-Rear Beam Lower Mounting<p>Part number 86636T6000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21097 Bracket - upper rear bumper side, left<p>Part number 86625T6000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21098 Bracket - upper rear bumper side, right<p>Part number 86626T6000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21099 Trim assembly - tail, left<p>Part number 866C1T6000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21100 Trim assembly - tail, right<p>Part number 866C2T6000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>