SELECT 
  cscart_discussion_posts.*, 
  cscart_discussion_messages.message, 
  cscart_discussion_rating.rating_value 
FROM 
  cscart_discussion_posts 
  LEFT JOIN cscart_discussion_messages ON cscart_discussion_messages.post_id = cscart_discussion_posts.post_id 
  LEFT JOIN cscart_discussion_rating ON cscart_discussion_rating.post_id = cscart_discussion_posts.post_id 
WHERE 
  cscart_discussion_posts.thread_id IN (50351) 
  AND cscart_discussion_posts.status = 'A' 
ORDER BY 
  cscart_discussion_posts.timestamp DESC 
LIMIT 
  0, 10

Query time 0.00077

JSON explain

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    "read_sorted_file": {
      "filesort": {
        "sort_key": "cscart_discussion_posts.`timestamp` desc",
        "table": {
          "table_name": "cscart_discussion_posts",
          "access_type": "ref",
          "possible_keys": ["thread_id", "thread_id_2"],
          "key": "thread_id_2",
          "key_length": "6",
          "used_key_parts": ["thread_id", "status"],
          "ref": ["const", "const"],
          "rows": 6,
          "filtered": 100,
          "index_condition": "cscart_discussion_posts.`status` = 'A'",
          "attached_condition": "cscart_discussion_posts.thread_id <=> 50351 and cscart_discussion_posts.`status` <=> 'A'"
        }
      }
    },
    "table": {
      "table_name": "cscart_discussion_messages",
      "access_type": "eq_ref",
      "possible_keys": ["PRIMARY"],
      "key": "PRIMARY",
      "key_length": "3",
      "used_key_parts": ["post_id"],
      "ref": ["cscart_migrate.cscart_discussion_posts.post_id"],
      "rows": 1,
      "filtered": 100
    },
    "table": {
      "table_name": "cscart_discussion_rating",
      "access_type": "eq_ref",
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      "used_key_parts": ["post_id"],
      "ref": ["cscart_migrate.cscart_discussion_posts.post_id"],
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    }
  }
}

Result

post_id thread_id name timestamp user_id ip_address status email message rating_value
118319 50351 Courtny 1456500540 0 38.104.13.154 A Perfect for a classic, nautical bathroom. 5
116583 50351 Dana 1445258700 0 71.178.243.75 A I used these flush mounts with the Atomic Sconces to create a nautical look in 2 guest baths. I absolutely recommend these fixtures for price, function and just because the customer service has been so great. 5
111340 50351 Laura 1433021640 0 184.151.61.43 A I just renovated a cabin at the cottage in a nautical theme. I used these as the reading lights for the bunkbeds. They look terrific! 5
110498 50351 Rich 1431911880 0 24.107.21.237 A Outfitted our newly renovated basement in red bulkheads -- round on ceiling and oval for wall sconces. Love 'em! Great splash of color and appropriately casual/ 5
103056 50351 Pat 1424106900 0 104.148.229.206 A This light sits just outside my patio doors. It gives me the beachy look I was looking for. 5
19967 50351 aeriel 1403214540 0 108.203.44.107 A I used this light in a beach house as sconces near 4 bunk beds, loved the galvanized metal finish and they looked great against the white walls. The shipping was quick and service from Barnlight Electric was great as usual! 5