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 (
    21197, 21198, 21199, 21200, 21201, 21202, 
    21203, 21204, 21205, 21206, 21207, 
    21208, 21209, 21210, 21211, 21212
  ) 
  AND cscart_product_descriptions.lang_code = 'en'

Query time 0.00190

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 (21197,21198,21199,21200,21201,21202,21203,21204,21205,21206,21207,21208,21209,21210,21211,21212) and cscart_product_descriptions.lang_code = 'en'"
    }
  }
}

Result

product_id short_description full_description unit_name
21197 Nut-Washer Assembly<p>Part number 878192H000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21198 Label-Fuel Economy<p>Part number 324302T034</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21199 Glass & Molding Assembly - Quarter Fixt, Left<p>Part number 87810T6CE0</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21200 Glass and Molding Assembly - Quarter Fixt, Right<p>Part number 87820T6000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21201 BOLT<p>Part number 88550C1000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21202 Control unit-free seat belt<p>Part number 888E0T6000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21203 Rear Slide-Cover End<p>Part number 88590B1100</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21204 Seat anchor bracket, left<p>Part number 888F0T6000DUE</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21205 Seat anchor bracket, right<p>Part number 888G0T6000DUE</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21206 Seat Belt Assembly - Front Left<p>Part number 888A0T6000DUE</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21207 Bolt-seatbelt anchor mounting<p>Part number 1911707287K</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21208 Seat Belt Assembly - Front Right<p>Part number 888B0T6000DUE</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21209 Buckle assembly - front seat belt, left<p>Part number 88830T6000DUE</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21210 Buckle assembly - front seat belt, right<p>Part number 88840T6000DUE</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21211 Stopper - upper seat belt<p>Part number 888773X000DUE</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21212 Stopper - lower seat belt<p>Part number 888781C000DUE</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>