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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 (
    18516, 51007, 51004, 51005, 51010, 51008, 
    51012, 51011, 51013, 51006, 51015, 
    51016, 51021, 51017, 51018, 51019
  ) 
  AND cscart_product_review_prepared_data.storefront_id = 1

Query time 0.00030

JSON explain

{
  "query_block": {
    "select_id": 1,
    "message": "Impossible WHERE noticed after reading const tables"
  }
}