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 (
    20973, 20974, 20975, 20976, 20977, 20978, 
    20979, 20980, 20981, 20982, 20983, 
    20984, 20985, 20986, 20987, 20988
  ) 
  AND cscart_product_descriptions.lang_code = 'ru'

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 (20973,20974,20975,20976,20977,20978,20979,20980,20981,20982,20983,20984,20985,20986,20987,20988) and cscart_product_descriptions.lang_code = 'ru'"
    }
  }
}

Result

product_id short_description full_description unit_name
20973 Speaker assembly - center<p>Part number 96350T1500</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
20974 Speaker & Protect Assembly-Front Door<p>Part number 96330T1500</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
20975 Speaker assembly - rear, left<p>Part number 96360T1500</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
20976 Speaker assembly - rear, right<p>Part number 96361T1500</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
20977 Speaker assembly - subwoofer, left<p>Part number 96380T1500NBD</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
20978 Speaker assembly - subwoofer, right<p>Part number 96380T1550NBD</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
20979 Horn Assembly - Low Pitch<p>Part number 96611T1000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
20980 Horn Assembly - High Pitch<p>Part number 96621T1000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
20981 Bolt-Washer Assembly<p>Part number 98131T4000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
20982 Rail spring-wiper blade, driver's seat<p>Part number 98355A9000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
20983 Blade assembly - wiper, driver's seat<p>Part number 98350O1000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
20984 Rail spring-wiper blade, passenger seat<p>Part number 983652S000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
20985 Blade assembly - wiper, passenger seat<p>Part number 98360F2600</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
20986 Motor & Pump - Windshield Washer, Front<p>Part number 985103T500</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
20987 Reservoir & Pump Assembly-Washer<p>Part number 98610T1000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
20988 Reservoir Assembly - Windshield Washer<p>Part number 98611T1000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>