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SELECT 
  cscart_product_descriptions.product_id, 
  cscart_product_descriptions.short_description, 
  IF(
    cscart_product_descriptions.short_description = '', 
    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 (
    5541, 5548, 5537, 5535, 5534, 5547, 5543, 
    5545, 5536, 5539, 5542, 5538, 5549, 
    5546, 5540, 5544, 6788, 6725, 6726, 
    6785, 6786, 6789, 6787
  ) 
  AND cscart_product_descriptions.lang_code = 'en'

Query time 0.00035

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": 23,
      "filtered": 100,
      "index_condition": "cscart_product_descriptions.product_id in (5541,5548,5537,5535,5534,5547,5543,5545,5536,5539,5542,5538,5549,5546,5540,5544,6788,6725,6726,6785,6786,6789,6787)",
      "attached_condition": "cscart_product_descriptions.lang_code = 'en'"
    }
  }
}

Result

product_id	short_description	full_description	meta_keywords	meta_description	search_words	promo_text
5534
5535
5536
5537
5538
5539
5540
5541
5542
5543
5544
5545
5546
5547
5548
5549
6725
6726
6785
6786
6787
6788
6789