Sandbox

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 
FROM 
  cscart_product_descriptions 
WHERE 
  cscart_product_descriptions.product_id IN (
    11488, 11491, 11499, 13783, 11526, 11523
  ) 
  AND cscart_product_descriptions.lang_code = 'en'

Query time 0.00042

JSON explain

{
  "query_block": {
    "select_id": 1,
    "table": {
      "table_name": "cscart_product_descriptions",
      "access_type": "range",
      "possible_keys": ["PRIMARY", "product_id"],
      "key": "product_id",
      "key_length": "3",
      "used_key_parts": ["product_id"],
      "rows": 6,
      "filtered": 100,
      "index_condition": "cscart_product_descriptions.product_id in (11488,11491,11499,13783,11526,11523)",
      "attached_condition": "cscart_product_descriptions.lang_code = 'en'"
    }
  }
}

Result

product_id	short_description	full_description
11488		<ul><li>A beautiful floral porcelain teapot </li><li>Dishwasher and microwave safe</li><li>For hot and cold liquids</li><li>1 l </li></ul> <p></p>
11491		<ul><li>Timeless Gin and Tonic cocktail glass </li></ul>
11499		<ul><li>24cm non stick pan</li><li>It has soft touch handle that allows for easy handling</li><li>Suitable for gas,electric and induction stoves</li></ul>
11523		<ul><li>Two wine glasses with a string design</li><li>Box of two </li></ul>
11526		<ul><li>Two flute glasses with a string design </li><li>Box of 2 flute glasses</li></ul>
13783