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 (
    20749, 20750, 20751, 20752, 20753, 20754, 
    20755, 20756, 20757, 20758, 20759, 
    20760, 20761, 20762, 20763, 20764
  ) 
  AND cscart_product_descriptions.lang_code = 'ru'

Query time 0.00045

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 (20749,20750,20751,20752,20753,20754,20755,20756,20757,20758,20759,20760,20761,20762,20763,20764) and cscart_product_descriptions.lang_code = 'ru'"
    }
  }
}

Result

product_id short_description full_description unit_name
20749 Trim Assembly - Rear Pillar Left<p>Part number 85850T1700NBD</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
20750 Trim assembly - center pillar lower, right<p>Part number 85845T1500NBD</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
20751 Cover assembly - engine room, left<p>Part number 861A0T1000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
20752 Cover assembly - engine room, right<p>Part number 861B0T1000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
20753 Molding assembly - windshield glass, lower part<p>Part number 86120T1000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
20754 Molding - Windshield, upper part<p>Part number 86121T1000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
20755 Bracket-windshield molding mounting, left<p>Part number 86137T1000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
20756 Bracket-windshield molding mounting, right<p>Part number 86147T1000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
20757 Cover Assembly - Cowl Top<p>Part number 86150T1000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
20758 Clip-Hood Seal Strip Mounting<p>Part number 86438A5000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
20759 Seal strip assembly - hood side, left<p>Part number 86470T1000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
20760 Seal Strip Assembly-Hood Side, Right<p>Part number 86480T1000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
20761 Garnish assembly-left<p>Part number 86130T1000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
20762 Garnish assembly-right<p>Part number 86140T1000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
20763 Coupler - Multi-function Camera<p>Part number 95761T1000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
20764 Nozzle Assembly-Windshield Washer<p>Part number 986303J000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>