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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 (
    20829, 20830, 20831, 20832, 20833, 20834, 
    20835, 20836, 20837, 20838, 20839, 
    20840, 20841, 20842, 20843, 20844
  ) 
  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 (20829,20830,20831,20832,20833,20834,20835,20836,20837,20838,20839,20840,20841,20842,20843,20844)"
    }
  }
}