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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 (
    21037, 21038, 21039, 21040, 21041, 21042, 
    21043, 21044, 21045, 21046, 21047, 
    21048, 21049, 21050, 21051, 21052
  ) 
  AND cscart_product_review_prepared_data.storefront_id = 0

Query time 0.00058

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 (21037,21038,21039,21040,21041,21042,21043,21044,21045,21046,21047,21048,21049,21050,21051,21052)"
    }
  }
}