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 (
    21583, 21584, 21585, 21586, 21587, 21588, 
    21589, 21590, 21591, 21592, 21593, 
    21594, 21595, 21596, 21597, 21598
  ) 
  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 (21583,21584,21585,21586,21587,21588,21589,21590,21591,21592,21593,21594,21595,21596,21597,21598) and cscart_product_descriptions.lang_code = 'ru'"
    }
  }
}

Result

product_id short_description full_description unit_name
21583 Fitting-coolant intake<p>Part number 256312T000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21584 radiator assembly<p>Part number 25310T1000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21585 radiator assembly<p>Part number 253L0T1000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21586 blower assembly<p>Part number 25380T1000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21587 Hose-radiator inlet<p>Part number 254L4T1000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21588 Hose-radiator outlet<p>Part number 254L5T1000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21589 Hose assembly - radiator, top<p>Part number 25414T1000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21590 Hose assembly - radiator, lower part<p>Part number 25415T1000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21591 Tank assembly - reservoir<p>Part number 25430T1000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21592 Cap - Radiator Reservoir<p>Part number 25441B1000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21593 Gasket - Radiator Reservoir Cap<p>Part number 254421D100</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21594 Hose Assembly - Water<p>Part number 25451T1000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21595 Hose Assembly - Degassing<p>Part number 254W0T1000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21596 level gauge<p>Part number 25448T1000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21597 band cable<p>Part number 915683E000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21598 Clamp-Hose<p>Part number 1471101036B</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>