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 (
    21069, 21070, 21071, 21072, 21073, 21074, 
    21075, 21076, 21077, 21078, 21079, 
    21080, 21081, 21082, 21083, 21084
  ) 
  AND cscart_product_descriptions.lang_code = 'en'

Query time 0.00034

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 (21069,21070,21071,21072,21073,21074,21075,21076,21077,21078,21079,21080,21081,21082,21083,21084) and cscart_product_descriptions.lang_code = 'en'"
    }
  }
}

Result

product_id short_description full_description unit_name
21069 Cover assembly - upper radiator grille<p>Part number 86390T6000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21070 Actuator - Active Air<p>Part number 86969T6000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21071 Flap & Duct Assemblies - Active Air<p>Part number 86950T6000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21072 Cover - front bumper, left<p>Part number 86597T6010</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21073 Bracket-front bumper side, left<p>Part number 86551T6000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21074 Cover - front bumper, right<p>Part number 86598T6010</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21075 Bracket - front bumper side, right<p>Part number 86552T6000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21076 Molding-Front Bumper License Plate<p>Part number 86519T6000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21077 Absorber-Front Bumper Energy<p>Part number 86521T6000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21078 Bracket-Reinforcement<p>Part number 86535T6000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21079 SKID PLATE-FR BUMPER<p>Part number 86577T6000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21080 Molding - front bumper, left<p>Part number 86595T6000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21081 Molding - front bumper, right<p>Part number 86596T6000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21082 Air duct-front bumper, left<p>Part number 86543T6000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21083 Air duct-front bumper, right<p>Part number 86544T6000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21084 End piece - air duct, left<p>Part number 86545T6000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>