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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 (
    19821, 19822, 19823, 19824, 19825, 19826, 
    19827, 19828, 19829, 19830, 19831, 
    19832, 19833, 19834, 19835, 19836
  ) 
  AND cscart_product_review_prepared_data.storefront_id = 0

Query time 0.00012

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 (19821,19822,19823,19824,19825,19826,19827,19828,19829,19830,19831,19832,19833,19834,19835,19836)"
    }
  }
}