MySQL RAND() 函數詳解：隨機數生成、種子固定、隨機排序實戰

基本用法

mysql> SELECT RAND(1), RAND(), RAND();
+------------------+------------------+------------------+
| RAND(1)          | RAND()           | RAND()           |
+------------------+------------------+------------------+
| 0.18109050223705 | 0.75023211143001 | 0.20788908117254 |
+------------------+------------------+------------------+

第一次調用傳入種子 RAND(1)，後續 RAND() 產生確定序列。同一會話中同種子序列固定，適用於測試、抽樣復現。

隨機排序：ORDER BY RAND()

SELECT * FROM tbl 
WHERE id >= (SELECT FLOOR(RAND() * (SELECT MAX(id) FROM tbl))) 
ORDER BY id LIMIT 10;

-- 1. 獲取總數
SELECT COUNT(*) INTO @total FROM tbl;
-- 2. 應用層生成隨機 offset，再 LIMIT offset, 10

-- 1~100
SELECT FLOOR(1 + RAND() * 100);

-- 10~20
SELECT FLOOR(10 + RAND() * 11);