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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 (
    21053, 21054, 21055, 21056, 21057, 21058, 
    21059, 21060, 21061, 21062, 21063, 
    21064, 21065, 21066, 21067, 21068
  ) 
  AND cscart_product_review_prepared_data.storefront_id = 0

Query time 0.00020

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 (21053,21054,21055,21056,21057,21058,21059,21060,21061,21062,21063,21064,21065,21066,21067,21068)"
    }
  }
}