Postgres函数返回数字0-7循环吗？

Question

How can I write a function which returns for example the numbers 0-7 round robin, in a "thread safe" manner ensuring a new number for each call (wrap around if > 7)?

It should be a global function so if "connection 1" calls it and gets the number 3, "connection 2" should get the number 4 when it calls and so on.

Answer 1

as per docs , you can cycle sequence:

t=# create sequence rr07 minvalue 0 maxvalue 7 cycle;
CREATE SEQUENCE
t=# select nextval('rr07');
 nextval
---------
       0
(1 row)

t=# select nextval('rr07');
 nextval
---------
       1
(1 row)

t=# select nextval('rr07');
 nextval
---------
       2
(1 row)

t=# select nextval('rr07');
 nextval
---------
       3
(1 row)

t=# select nextval('rr07');
 nextval
---------
       4
(1 row)

t=# select nextval('rr07');
 nextval
---------
       5
(1 row)

t=# select nextval('rr07');
 nextval
---------
       6
(1 row)

t=# select nextval('rr07');
 nextval
---------
       7
(1 row)

t=# select nextval('rr07');
 nextval
---------
       0
(1 row)