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 (
    21663, 21664, 21665, 21666, 21667, 21668, 
    21669, 21670, 21671, 21672, 21673, 
    21674, 21675, 21676, 21677, 21678
  ) 
  AND cscart_product_descriptions.lang_code = 'ru'

Query time 0.00046

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 (21663,21664,21665,21666,21667,21668,21669,21670,21671,21672,21673,21674,21675,21676,21677,21678) and cscart_product_descriptions.lang_code = 'ru'"
    }
  }
}

Result

product_id short_description full_description unit_name
21663 Insulator-Strut<p>Part number 55310T1000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21664 spring-rear<p>Part number 55330T1000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21665 Crossmember-rear<p>Part number 55405T1001</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21666 Damper Assembly - Rear Dynamic<p>Part number 55499T1000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21667 Cap-bleeder screw<p>Part number 58314T1200</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21668 Brake assembly-rear wheel, left<p>Part number 58210T1100</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21669 Brake assembly-rear wheel, right<p>Part number 58230T1100</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21670 Caliper Kit - Rear Brake, Left<p>Part number 58310T1A10</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21671 Caliper Kit - Rear Brake, Right<p>Part number 58311T1A10</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21672 Pad Kit - Rear Disc Brake<p>Part number 58302T1A10</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21673 Holder - Fuel Tube<p>Part number 31354T1000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21674 Holder - Fuel Tube<p>Part number 31356T1000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21675 Tube-hydronic unit two front, right<p>Part number 58711T1000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21676 Tube-Hydraulic Module to Connector Left<p>Part number 58712T4000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21677 Tube-Hydraulic Module to Connector Right<p>Part number 58713T4000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21678 Tube assembly - brake<p>Part number 58714T4000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>