Postgres 文本列只有 allows/converts 小写并且没有特殊字符，例如：Ñöáè

Question

我有一个 table，我希望该 1 列只接受小写字符串并且没有特殊字符，例如 Ñóáöäë 等...

是否可以将此约束添加到列中？

CREATE TABLE lawyer (
  id SERIAL PRIMARY KEY,
  name VARCHAR NOT NULL,
  url_name VARCHAR NOT NULL,
  gender VARCHAR(1) check (gender in ('m','f')) NOT NULL
);

我要添加约束的列是url_name

Answer 1

将所需的字符放入此 translate() 调用的第二个参数中：

CREATE TABLE lawyer (
  id SERIAL PRIMARY KEY,
  name VARCHAR NOT NULL,
  url_name VARCHAR check(translate(url_name, 'abcdefghijklmnopqrstuvwxyz', '') = '') NOT NULL,
  gender VARCHAR(1) check (gender in ('m','f')) NOT NULL
);

insert into lawyer
values (default, 'Adam Smith', 'domain', 'f');

INSERT 0 1

insert into lawyer
values (default, 'Adam Smith', 'dömain', 'f');

ERROR:  new row for relation "lawyer" violates check constraint "lawyer_url_name_check"
DETAIL:  Failing row contains (3, Adam Smith, dömain, f).

---

或者，您可以创建一个触发器，它会即时修改值：

create or replace function lawyer_before_insert_or_update()
returns trigger language plpgsql as $$
begin
    new.url_name := lower(new.url_name);
    if translate(new.url_name, 'abcdefghijklmnopqrstuvwxyz', '') <> '' then
        raise exception 'Incorrect url name.';
    end if;
    return new;
end $$;

create trigger lawyer_before_insert_or_update
before insert or update on lawyer
for each row execute procedure lawyer_before_insert_or_update();

insert into lawyer
values (default, 'Adam Smith', 'DOMAIN', 'f')
returning *;

 id |    name    | url_name | gender 
----+------------+----------+--------
  4 | Adam Smith | domain   | f
(1 row)

INSERT 0 1

insert into lawyer
values (default, 'Adam Smith', 'dömain', 'f');

ERROR:  Incorrect url name.

Answer 2

对于转换（例如转换为小写），我同意触发器。但是，对于允许的字符，如果这是一个经常性的要求，我建议使用域。

类似于：

 create domain lower_ascii AS text check VALUE ~ '^[a-z]*$';

域有几个优点，包括它们提供跨所有用途的单一管理点，如果需求发生变化，您可以全局修改检查约束。