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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 (
    21647, 21648, 21649, 21650, 21651, 21652, 
    21653, 21654, 21655, 21656, 21657, 
    21658, 21659, 21660, 21661, 21662
  ) 
  AND cscart_product_review_prepared_data.storefront_id = 0

Query time 0.00018

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 (21647,21648,21649,21650,21651,21652,21653,21654,21655,21656,21657,21658,21659,21660,21661,21662)"
    }
  }
}