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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 (
    21935, 21936, 21937, 21938, 21939, 21940, 
    21941, 21942, 21943, 21944, 21945, 
    21946, 21947, 21948, 21949, 21950
  ) 
  AND cscart_product_review_prepared_data.storefront_id = 0

Query time 0.00015

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 (21935,21936,21937,21938,21939,21940,21941,21942,21943,21944,21945,21946,21947,21948,21949,21950)"
    }
  }
}