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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 (
    21101, 21102, 21103, 21104, 21105, 21106, 
    21107, 21108, 21109, 21110, 21111, 
    21112, 21113, 21114, 21115, 21116
  ) 
  AND cscart_product_review_prepared_data.storefront_id = 0

Query time 0.00019

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 (21101,21102,21103,21104,21105,21106,21107,21108,21109,21110,21111,21112,21113,21114,21115,21116)"
    }
  }
}