首先 random() 函数用于生成 0-1 之间的随机数
postgres=# SELECT random() as rand;
rand
--------------------
0.6296923727161818
(1 row)
取整函数有 ceil() floor() trunc()
postgres=# SELECT ceil(1.5) as ceil, floor(1.5) as floor, trunc(1.5) as trunc;
ceil | floor | trunc
------+-------+-------
2 | 1 | 1
(1 row)
将以上两个函数结合起来就可以生成随机整数
-- 生成 1-10 之间的整数
postgres=# SELECT ceil(random() * 10) as randint;
randint
---------
4
(1 row)
generate_series() 用于生成一连串整数
postgres=# SELECT generate_series(1,3);
generate_series
-----------------
1
2
3
(3 rows)
postgres=# SELECT num FROM generate_series(1,3) AS series(num);
num
-----
1
2
3
(3 rows)
可用于重复查询
-- 重复 3 次打印当前时间(generate_series 步长为2)
postgres=# SELECT current_timestamp FROM generate_series(1,5,2);
current_timestamp
-------------------------------
2021-07-20 10:31:13.037552+08
2021-07-20 10:31:13.037552+08
2021-07-20 10:31:13.037552+08
(3 rows)
生成多个随机整数
10 个 1-10 之间的整数(有重复)
postgres=# SELECT ceil(random() * 10) AS num FROM generate_series(1,10);
num
-----
4
2
6
5
2
6
8
1
5
8
(10 rows)
5 个 1-10 之间的整数(无重复)
postgres=# SELECT num FROM generate_series(1,10) AS series(num) ORDER BY random() LIMIT 5;
num
-----
6
5
3
7
8
(5 rows)
————————————————
版权声明：本文为CSDN博主「jiang_huixin」的原创文章，遵循CC 4.0 BY-SA版权协议，转载请附上原文出处链接及本声明。
原文链接：https://blog.csdn.net/jiang_huixin/article/details/118930113