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 (
    20701, 20702, 20703, 20704, 20705, 20706, 
    20707, 20708, 20709, 20710, 20711, 
    20712, 20713, 20714, 20715, 20716
  ) 
  AND cscart_product_descriptions.lang_code = 'en'

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 (20701,20702,20703,20704,20705,20706,20707,20708,20709,20710,20711,20712,20713,20714,20715,20716) and cscart_product_descriptions.lang_code = 'en'"
    }
  }
}

Result

product_id short_description full_description unit_name
20701 Bezel-Crush Pad Garnish Center<p>Part number 847C2T1000OWN</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
20702 Cover assembly - fuse box<p>Part number 84753T1000OWN</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
20703 Shroud-lower steering column<p>Part number 84852T1100NBD</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
20704 Panel Assembly - Cluster Fascia<p>Part number 84830T1100NBD</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
20705 Bracket - Smart Key Mounting<p>Part number 847B2T1000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
20706 Lamp Assembly-Luggage & Glove<p>Part number 92601G8000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
20707 Switch Assembly - Trunk Lid Opener<p>Part number 93550B1100</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
20708 Switch Assemblies - Tilt & Telescopic<p>Part number 93691T1000NBD</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
20709 Switch Assembly - Side Crash Pad<p>Part number 93700T1650OWN</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
20710 Switch Assembly - Hazard<p>Part number 93790T1000VCS</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
20711 Cover assembly-under, left<p>Part number 84590T1000NNB</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
20712 Duct Assembly - Center Air Vent<p>Part number 97410T10004X</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
20713 Cover Assembly - Indirect Vent<p>Part number 97461T1000NBD</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
20714 Duct assembly - side air vent, left<p>Part number 97480T10004X</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
20715 Cover-defrost nozzle<p>Part number 97353T1000NBD</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
20716 Sun visor assembly, left<p>Part number 85210T1BF0NBD</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>