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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, 
  cscart_product_descriptions.unit_name 
FROM 
  cscart_product_descriptions 
WHERE 
  cscart_product_descriptions.product_id IN (
    657, 376, 540, 592, 1015, 767, 1088, 572, 
    619, 355, 342, 547
  ) 
  AND cscart_product_descriptions.lang_code = 'en'

Query time 0.00077

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": 12,
      "filtered": 100,
      "index_condition": "cscart_product_descriptions.product_id in (657,376,540,592,1015,767,1088,572,619,355,342,547) and cscart_product_descriptions.lang_code = 'en'"
    }
  }
}

Result

product_id	short_description	full_description	meta_keywords	meta_description	search_words	promo_text	unit_name
342
355
376
540
547
572
592
619
657
767
1015
1088