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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 (
    20813, 20814, 20815, 20816, 20817, 20818, 
    20819, 20820, 20821, 20822, 20823, 
    20824, 20825, 20826, 20827, 20828
  ) 
  AND cscart_product_review_prepared_data.storefront_id = 0

Query time 0.00017

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 (20813,20814,20815,20816,20817,20818,20819,20820,20821,20822,20823,20824,20825,20826,20827,20828)"
    }
  }
}