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法律研究如何在 MySQL 中從最近的 20 行資料中隨機選擇 5 行？
要獲得隨機選擇，使用 RAND() 方法。要限制行數，使用 LIMIT() 方法。
讓我們首先建立一個表 −
mysql> create table DemoTable -> ( -> ShippingDate datetime -> ); Query OK, 0 rows affected (0.51 sec)
使用 insert 命令向表中插入一些記錄 −
mysql> insert into DemoTable values('2019-01-01');
Query OK, 1 row affected (0.11 sec)
mysql> insert into DemoTable values('2019-01-03');
Query OK, 1 row affected (0.14 sec)
mysql> insert into DemoTable values('2019-01-05');
Query OK, 1 row affected (0.13 sec)
mysql> insert into DemoTable values('2019-01-07');
Query OK, 1 row affected (0.11 sec)
mysql> insert into DemoTable values('2019-02-02');
Query OK, 1 row affected (0.15 sec)
mysql> insert into DemoTable values('2019-02-04');
Query OK, 1 row affected (0.14 sec)
mysql> insert into DemoTable values('2019-02-12');
Query OK, 1 row affected (0.07 sec)
mysql> insert into DemoTable values('2019-02-24');
Query OK, 1 row affected (0.14 sec)
mysql> insert into DemoTable values('2019-02-25');
Query OK, 1 row affected (0.11 sec)
mysql> insert into DemoTable values('2019-03-10');
Query OK, 1 row affected (0.16 sec)
mysql> insert into DemoTable values('2019-03-11');
Query OK, 1 row affected (0.11 sec)
mysql> insert into DemoTable values('2019-03-12');
Query OK, 1 row affected (0.10 sec)
mysql> insert into DemoTable values('2019-03-14');
Query OK, 1 row affected (0.11 sec)
mysql> insert into DemoTable values('2019-03-16');
Query OK, 1 row affected (0.15 sec)
mysql> insert into DemoTable values('2019-03-18');
Query OK, 1 row affected (0.18 sec)
mysql> insert into DemoTable values('2019-03-20');
Query OK, 1 row affected (0.14 sec)
mysql> insert into DemoTable values('2019-03-25');
Query OK, 1 row affected (0.16 sec)
mysql> insert into DemoTable values('2019-03-28');
Query OK, 1 row affected (0.15 sec)
mysql> insert into DemoTable values('2019-03-29');
Query OK, 1 row affected (0.18 sec)
mysql> insert into DemoTable values('2019-04-03');
Query OK, 1 row affected (0.20 sec)
mysql> insert into DemoTable values('2019-04-03');
Query OK, 1 row affected (0.13 sec)
mysql> insert into DemoTable values('2019-04-04');
Query OK, 1 row affected (0.14 sec)
mysql> insert into DemoTable values('2019-04-06');
Query OK, 1 row affected (0.16 sec)
mysql> insert into DemoTable values('2019-04-09');
Query OK, 1 row affected (0.15 sec)
mysql> insert into DemoTable values('2019-05-01');
Query OK, 1 row affected (0.23 sec)
mysql> insert into DemoTable values('2019-05-13');
Query OK, 1 row affected (0.24 sec)
mysql> insert into DemoTable values('2019-05-15');
Query OK, 1 row affected (0.15 sec)
mysql> insert into DemoTable values('2019-05-16');
Query OK, 1 row affected (0.16 sec)
mysql> insert into DemoTable values('2019-05-18');
Query OK, 1 row affected (0.20 sec)使用 select 語句顯示錶中的所有記錄 −
mysql> select *from DemoTable;
輸出
這將產生以下輸出 −
+---------------------+ | ShippingDate | +---------------------+ | 2019-01-01 00:00:00 | | 2019-01-03 00:00:00 | | 2019-01-05 00:00:00 | | 2019-01-07 00:00:00 | | 2019-02-02 00:00:00 | | 2019-02-04 00:00:00 | | 2019-02-12 00:00:00 | | 2019-02-24 00:00:00 | | 2019-02-25 00:00:00 | | 2019-03-10 00:00:00 | | 2019-03-11 00:00:00 | | 2019-03-12 00:00:00 | | 2019-03-14 00:00:00 | | 2019-03-16 00:00:00 | | 2019-03-18 00:00:00 | | 2019-03-20 00:00:00 | | 2019-03-25 00:00:00 | | 2019-03-28 00:00:00 | | 2019-03-29 00:00:00 | | 2019-04-03 00:00:00 | | 2019-04-03 00:00:00 | | 2019-04-04 00:00:00 | | 2019-04-06 00:00:00 | | 2019-04-09 00:00:00 | | 2019-05-01 00:00:00 | | 2019-05-13 00:00:00 | | 2019-05-15 00:00:00 | | 2019-05-16 00:00:00 | | 2019-05-18 00:00:00 | +---------------------+ 29 rows in set (0.00 sec)
以下是從最近 20 行中隨機選擇 5 行的查詢 −
mysql> select tbl1.* from (select *from DemoTable ORDER BY ShippingDate DESC LIMIT 20 ) as tbl1 -> ORDER BY RAND() LIMIT 5;
輸出
這將產生以下輸出 −
+---------------------+ | ShippingDate | +---------------------+ | 2019-03-14 00:00:00 | | 2019-05-13 00:00:00 | | 2019-03-25 00:00:00 | | 2019-05-16 00:00:00 | | 2019-03-10 00:00:00 | +---------------------+ 5 rows in set (0.04 sec)
更新於：2020 年 6 月 30 日
423 次瀏覽
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