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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 (
    20781, 20782, 20783, 20784, 20785, 20786, 
    20787, 20788, 20789, 20790, 20791, 
    20792, 20793, 20794, 20795, 20796
  ) 
  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 (20781,20782,20783,20784,20785,20786,20787,20788,20789,20790,20791,20792,20793,20794,20795,20796)"
    }
  }
}