在postgreSQL上创建一个字符序列

Question

所以，我在表列上引用了这个序列，每次我插入时它的值由nextval('ptable_pr_codigo_seq'::regclass)定义

CREATE SEQUENCE public.ptable_pr_codigo_seq
  INCREMENT 1
  MINVALUE 1
  MAXVALUE 9223372036854775807
  START 103
  CACHE 1;
ALTER TABLE public.ptable_pr_codigo_seq
  OWNER TO postgres;

现在，我怎样才能创建一个新序列，所以每次插入时，值都不是数字而是[A~ZZZ]范围内的字符？

Example: First insert column value = A
         Second                    = B
         Third                     = C
         27th                      = AA
         ...
         ?Th                       = ZZZ

Answer 1

接受挑战 ;）

我认为只有PostgreSQL序列机制（1）才有办法做到这一点但是如果你真的需要这样的东西（我对你为什么需要这样的东西很感兴趣），你可以做一个能让你回归的功能您想要的下一个值并将其放入触发器中。

例如，首先创建一个表：

create table test (test_id varchar);

使用下面这样的功能

create or replace function next_id_test()
 returns trigger language plpgsql as $function$
begin
    with cte_conform_char_list as
    (
        select val, row_number() over (order by val), lead(val) over (order by val)
        from (values ('A'), ('B'), ('C'), ('D'), ('E'), ('F')) as t(val) -- you can continue this list as much as you want it ;)
        order by 1
    )
    , cte_built_char_list as
    (
        select 
            cte.val
            , cte.row_number
            , coalesce(cte.lead, cte_2.val) as next_char
        from cte_conform_char_list cte
            left outer join cte_conform_char_list cte_2
                on cte_2.row_number = cte.row_number - (select max(row_number) from cte_conform_char_list) +1
    )
    select 
        case 
            when row_number < (select max(row_number) from cte_built_char_list)
                then repeat(next_char, cast(rank() over (partition by row_number order by test_id) as int)) 
                else repeat(next_char, cast(rank() over (partition by row_number order by test_id) + 1 as int))
        end as next_test_id into new.test_id
    from test T
        inner join cte_built_char_list cte on substring(T.test_id from 1 for 1) = cte.val
    order by char_length(test_id), test_id;

    return new;
end;
$function$;

将功能附加到触发前

create trigger tg_test before insert on test for each row execute procedure next_id_test();

插入一个并不重要的值（无论如何都会改变）

insert into test values ('ttt');

然后你可以观察到你有正确的性格。

select *
from test;

我知道这有点重，但我没有看到任何其他的。功能可能不完美，但我没有很多时间:)

希望它会帮助你;）