Mysql：'由Rand（）限制4的訂單'？

Question

我需要從最新新聞數據庫中隨機抽取4個項目。

因為該表有很多行。 用RAND（）進行排序或浪費資源是否明智？因為它將遍歷整個表並對它重新排序？

有更好的方法嗎？ 從具有數百行的表中提取隨機特征項？

例：

$l=$database->query("SELECT car,price,thumbnail FROM cardb WHERE type='new' order by RAND() LIMIT 4");
foreach($l as $l){print_r($l);}

感謝您抽出時間來回答}

Answer 1

好吧...我將在兩個查詢中執行此操作。 獲取隨機行號：

SELECT
    floor(count * rand()) r1,
    floor(count * rand()) r2,
    floor(count * rand()) r3,
    floor(count * rand()) r4
FROM
    (SELECT count(*) count FROM cardb WHERE type = 'new') c

並獲取行：

SELECT car, price, thumbnail FROM cardb WHERE type = 'new' LIMIT {r1}, 1
UNION ALL
SELECT car, price, thumbnail FROM cardb WHERE type = 'new' LIMIT {r2}, 1
UNION ALL
SELECT car, price, thumbnail FROM cardb WHERE type = 'new' LIMIT {r3}, 1
UNION ALL
SELECT car, price, thumbnail FROM cardb WHERE type = 'new' LIMIT {r4}, 1