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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.meta_keywords, 
  cscart_product_descriptions.meta_description, 
  cscart_product_descriptions.search_words, 
  cscart_product_descriptions.promo_text 
FROM 
  cscart_product_descriptions 
WHERE 
  cscart_product_descriptions.product_id IN (289, 294) 
  AND cscart_product_descriptions.lang_code = 'en'

Query time 0.00052

JSON explain

{
  "query_block": {
    "select_id": 1,
    "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"],
      "rows": 2,
      "filtered": 100,
      "index_condition": "((cscart_product_descriptions.product_id in (289,294)) and (cscart_product_descriptions.lang_code = 'en'))"
    }
  }
}

Result

product_id	short_description	full_description	meta_keywords	meta_description	search_words	promo_text
289		<p>Wrecking 1999 Ford AU XR6</p><p>6cyl Auto</p>			Ford,Xr6
294					2013 ,Ford ,Focus ,Petrol ,Manual