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 (
    20829, 20830, 20831, 20832, 20833, 20834, 
    20835, 20836, 20837, 20838, 20839, 
    20840, 20841, 20842, 20843, 20844
  ) 
  AND cscart_product_descriptions.lang_code = 'ru'

Query time 0.00031

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 (20829,20830,20831,20832,20833,20834,20835,20836,20837,20838,20839,20840,20841,20842,20843,20844) and cscart_product_descriptions.lang_code = 'ru'"
    }
  }
}

Result

product_id short_description full_description unit_name
20829 Camera assembly - side view, left<p>Part number 99220T1010</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
20830 Camera assembly - side view, right<p>Part number 99230T1010</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
20831 Clip<p>Part number 1420214120B</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
20832 Film-anti-chipping left<p>Part number 877F5T1000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
20833 Film-Anti Chopping Right<p>Part number 877F6T1000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
20834 Clip-Westline Molding Mounting<p>Part number 87759T1000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
20835 Clip-Westline Molding Mounting<p>Part number 877E9T1000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
20836 Clip-side sill molding mounting<p>Part number 87758D2000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
20837 Molding assembly - side sill, left<p>Part number 87751T1001MDY</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
20838 Molding assembly - side sill, right<p>Part number 87752T1001MDY</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
20839 Seat anchor bracket, left<p>Part number 888F0T1000NBD</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
20840 Seat anchor bracket, right<p>Part number 888G0T1000NBD</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
20841 Seat Belt Assembly - Front Left<p>Part number 888A0T1000NWA</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
20842 Seat Belt Assembly - Front Right<p>Part number 888B0T1000NWA</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
20843 Stopper - upper seat belt<p>Part number 888773X000NWA</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
20844 Stopper - lower seat belt<p>Part number 888781C000NWA</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>