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 (
    486457, 486547, 487447, 496449, 586443, 
    586445, 586447, 586449, 586451, 586453, 
    586455, 586457
  ) 
  AND cscart_product_descriptions.lang_code = 'en'

Query time 0.00192

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost": 0.0216566,
    "nested_loop": [
      {
        "table": {
          "table_name": "cscart_product_descriptions",
          "access_type": "range",
          "possible_keys": ["PRIMARY", "product_id"],
          "key": "PRIMARY",
          "key_length": "9",
          "used_key_parts": ["product_id", "lang_code"],
          "loops": 1,
          "rows": 12,
          "cost": 0.0216566,
          "filtered": 100,
          "attached_condition": "cscart_product_descriptions.product_id in (486457,486547,487447,496449,586443,586445,586447,586449,586451,586453,586455,586457) and cscart_product_descriptions.lang_code = 'en'"
        }
      }
    ]
  }
}