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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 (
    21775, 21776, 21777, 21778, 21779, 21780, 
    21781, 21782, 21783, 21784, 21785, 
    21786, 21787, 21788, 21789, 21790
  ) 
  AND cscart_product_review_prepared_data.storefront_id = 0

Query time 0.00011

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 (21775,21776,21777,21778,21779,21780,21781,21782,21783,21784,21785,21786,21787,21788,21789,21790)"
    }
  }
}