问PostgreSQL分配随机的、非重复的值

EN

create or replace function fun(topic_id int) returns bool as
$$
declare
st_count int;
topic_count int;
begin
select count(*) into st_count from student;
select n_tasks into topic_count from topic where topicid=topic_id;

if st_count=topic_count and st_count>0 and topic_count>0 then
execute format('create table %I (first_name varchar, task int)','topic'||topic_id);
execute format('insert into %I select name,row_number() over (order by random()) rn from student','topic'||topic_id);
return true;
end if;


if st_count>topic_count and st_count>0 and topic_count>0 then
execute format('create table %I (first_name varchar, task int)','topic'||topic_id);
execute format('insert into %I 
with cte as (select generate_series(1,%s) rn), 
cte1 as (
select row_number() over (order by random()) rn, 
name from student t1) select t1.name, coalesce(t2.rn,round(random()* %s)) 
from cte1 t1 left join cte t2 on t1.rn=t2.rn',
'topic'||topic_id,topic_count,topic_count);

return true;
end if;

if st_count<topic_count and st_count>0 and topic_count>0 then
execute format('create table %I (first_name varchar, task int)','topic'||topic_id);
execute format('insert into %I with cte as (select generate_series(1,%s) rn),
cte1 as (select row_number() over (order by random()) rn, name from student t1),
cte2 as (select coalesce(t2.rn, round(random()* %s)) rn_,t1.rn from cte t1 
left join cte1 t2 on t1.rn=t2.rn) 
select t1.name,t2.rn from cte2 t2 inner join cte1 t1 on t1.rn=t2.rn_',
'topic'||topic_id,topic_count,st_count);

return true;
end if;


return false;
end;

$$
language plpgsql

select fun(topicid) from topic;