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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 (
    21679, 21680, 21681, 21682, 21683, 21684, 
    21685, 21686, 21687, 21688, 21689, 
    21690, 21691, 21692, 21693, 21694
  ) 
  AND cscart_product_review_prepared_data.storefront_id = 0

Query time 0.00024

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 (21679,21680,21681,21682,21683,21684,21685,21686,21687,21688,21689,21690,21691,21692,21693,21694)"
    }
  }
}