SELECT 
  cscart_product_descriptions.product_id, 
  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 (42, 40, 37, 43) 
  AND cscart_product_descriptions.lang_code = 'en'

Query time 0.00066

JSON explain

{
  "query_block": {
    "select_id": 1,
    "nested_loop": [
      {
        "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": 4,
          "filtered": 100,
          "index_condition": "cscart_product_descriptions.product_id in (42,40,37,43)",
          "attached_condition": "cscart_product_descriptions.lang_code = 'en'"
        }
      }
    ]
  }
}