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SELECT 
  cscart_product_review_prepared_data.product_id AS product_id, 
  cscart_product_review_prepared_data.average_rating AS average_rating, 
  cscart_product_review_prepared_data.reviews_count AS reviews_count 
FROM 
  cscart_product_review_prepared_data 
WHERE 
  cscart_product_review_prepared_data.product_id IN (
    21423, 21424, 21425, 21426, 21427, 21428, 
    21429, 21430, 21431, 21432, 21433, 
    21434, 21435, 21436, 21437, 21438
  ) 
  AND cscart_product_review_prepared_data.storefront_id = 0

Query time 0.00016

JSON explain

{
  "query_block": {
    "select_id": 1,
    "table": {
      "table_name": "cscart_product_review_prepared_data",
      "access_type": "ALL",
      "possible_keys": ["PRIMARY"],
      "rows": 5,
      "filtered": 100,
      "attached_condition": "cscart_product_review_prepared_data.storefront_id = 0 and cscart_product_review_prepared_data.product_id in (21423,21424,21425,21426,21427,21428,21429,21430,21431,21432,21433,21434,21435,21436,21437,21438)"
    }
  }
}