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 (
    21309, 21310, 21311, 21312, 21313, 21314, 
    21315, 21316, 21317, 21318, 21319, 
    21320, 21321, 21322, 21325, 21326
  ) 
  AND cscart_product_descriptions.lang_code = 'ru'

Query time 0.00040

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 (21309,21310,21311,21312,21313,21314,21315,21316,21317,21318,21319,21320,21321,21322,21325,21326) and cscart_product_descriptions.lang_code = 'ru'"
    }
  }
}

Result

product_id short_description full_description unit_name
21309 Garnish-side repeater upper, right<p>Part number 923A8T6010</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21310 Garnish-side repeater upper, right<p>Part number 923A8T6000UYH</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21311 Garnish-side repeater lower, left<p>Part number 923B7T6010</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21312 Garnish-side repeater lower, left<p>Part number 923B7T6000UYH</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21313 Garnish-side repeater lower, right<p>Part number 923B8T6010</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21314 Garnish-side repeater lower, right<p>Part number 923B8T6000UYH</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21315 Lamp assembly - side repeater upper, left<p>Part number 923A1T6000UYH</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21316 Lamp assembly - side repeater upper, right<p>Part number 923A2T6000UYH</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21317 Lamp assembly - side repeater lower, left<p>Part number 923B1T6000UYH</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21318 Lamp assembly - side repeater lower, right<p>Part number 923B2T6000UYH</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21319 Clip<p>Part number 1421206000N</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21320 retainer<p>Part number 8691022000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21321 Moisture Absorbant<p>Part number 92125J2000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21322 Dust Cover-Headhamp<p>Part number 92140J2000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21325 Flange cover-rear combination outside, left<p>Part number 92411T6000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21326 Flange cover-rear combination outside, right<p>Part number 92421T6000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>