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 (
    21037, 21038, 21039, 21040, 21041, 21042, 
    21043, 21044, 21045, 21046, 21047, 
    21048, 21049, 21050, 21051, 21052
  ) 
  AND cscart_product_descriptions.lang_code = 'en'

Query time 0.00037

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 (21037,21038,21039,21040,21041,21042,21043,21044,21045,21046,21047,21048,21049,21050,21051,21052) and cscart_product_descriptions.lang_code = 'en'"
    }
  }
}

Result

product_id short_description full_description unit_name
21037 Hose assembly - water inlet<p>Part number 97311T1300</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21038 Hose Assembly - Water Outlet<p>Part number 97312T1300</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21039 Duct - rear heating, left<p>Part number 97360T1000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21040 Duct-rear heating rear, left<p>Part number 97365T1000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21041 Duct-rear heating rear, right<p>Part number 97375T1000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21042 Duct - rear heating, right<p>Part number 97370T1000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21043 Cover Assembly - Air Filter<p>Part number 971A9T6010</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21044 Control Assembly - Heater<p>Part number 97250T1030UV2</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21045 Bracket-Ambient Sensor Mounting<p>Part number 97281T1000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21046 O-ring<p>Part number 9796034350</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21047 Tube Assemblies - Suction & Liquid<p>Part number 97775T1100</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21048 Cover assembly - engine room, left<p>Part number 861A0T6000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21049 Cover assembly - engine room, right<p>Part number 861B0T6000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21050 Molding-Windshield Glass<p>Part number 86120T6000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21051 Molding - Windshield, upper part<p>Part number 86121T6000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21052 Bracket-windshield molding mounting, left<p>Part number 86137T6000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>