插入值(generate_series) -我如何重用/循环数字，例如，1,2,3,1,2,3

Question

我使用generate_series在表中插入值。并且generate_series在其范围内插入指定的值。

例如

:对于下面的查询，

SELECT i AS id, i AS age, i AS house_number
INTO egg
FROM generate_Series(1,6) AS i;

我们得到的结果是:

id  age  house_number
1   1    1
2   2    2
3   3    3
4   4    4
5   5    5
6   6    6

但我的问题是，我想只插入到第3列"年龄"，然后从0开始后3:

id  age  house_number
1   1    1
2   2    2
3   3    3
4   1    4
5   2    5
6   3    6

这可能吗?generate_series()中是否有一些随机函数执行相同的功能?

Answer 1

您可以使用模运算从0循环到n - 1并加1:

SELECT i AS id, (i - 1) % 3 +1 AS age, i AS house_number
INTO egg
FROM generate_Series(1,6) AS i;

Answer 2

您可以使用设计的序列来做到这一点:

create table test (id serial);
alter sequence test_id_seq cycle minvalue 0 maxvalue 3 start 0 restart;
insert into test values(DEFAULT);
insert into test values(DEFAULT);
insert into test values(DEFAULT);
insert into test values(DEFAULT);
insert into test values(DEFAULT);
insert into test values(DEFAULT);
insert into test values(DEFAULT);
insert into test values(DEFAULT);
select * from test;
 id 
----
  0
  1
  2
  3
  0
  1
  2
  3
(8 rows)