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 (
    21471, 21472, 21473, 21474, 21475, 21476, 
    21477, 21478, 21479, 21480, 21481, 
    21482, 21483, 21484, 21485, 21486
  ) 
  AND cscart_product_descriptions.lang_code = 'ru'

Query time 0.00039

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 (21471,21472,21473,21474,21475,21476,21477,21478,21479,21480,21481,21482,21483,21484,21485,21486) and cscart_product_descriptions.lang_code = 'ru'"
    }
  }
}

Result

product_id short_description full_description unit_name
21471 Cover Assay-Under<p>Part number 97285T6000UBL</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21472 Hose assembly - water inlet<p>Part number 97311T6500</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21473 Grommet-Heater Pipe<p>Part number 97313G2000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21474 Pipe-water inlet<p>Part number 97553T6100</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21475 Hose Assembly - Water Outlet<p>Part number 97312T6500</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21476 Hose-water intake<p>Part number 97541T6000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21477 Hose-water intake<p>Part number 97551T6000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21478 Hose-water intake<p>Part number 97561T6000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21479 Hose-water outlet<p>Part number 97542T6000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21480 Hose-water outlet<p>Part number 97552T6000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21481 Hose-water outlet<p>Part number 97562T6000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21482 Pad-water hose<p>Part number 97331T6500</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21483 Fife-Water Outlet<p>Part number 97554T6100</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21484 Quick Connector-Hose<p>Part number 97333T6000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21485 Duct - rear heating, left<p>Part number 97360T6000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21486 Duct-rear heating rear, left<p>Part number 97365T6000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>