url 的 postgresql 唯一非连续 id

Question

我看过一些在 Stackoverflow 上创建字母数字 ID 的方法，但它们都有自己的弱点，有些没有检查冲突，有些使用的序列在使用逻辑复制时不是一个好的选择。

谷歌搜索后我找到了this具有以下脚本的网站，该脚本检查冲突并且不使用序列。然而，这是在表中插入一行时作为触发器完成的。

-- Create a trigger function that takes no arguments.
-- Trigger functions automatically have OLD, NEW records
-- and TG_TABLE_NAME as well as others.
CREATE OR REPLACE FUNCTION unique_short_id()
RETURNS TRIGGER AS $$

 -- Declare the variables we'll be using.
DECLARE
  key TEXT;
  qry TEXT;
  found TEXT;
BEGIN

  -- generate the first part of a query as a string with safely
  -- escaped table name, using || to concat the parts
  qry := 'SELECT id FROM ' || quote_ident(TG_TABLE_NAME) || ' WHERE id=';

  -- This loop will probably only run once per call until we've generated
  -- millions of ids.
  LOOP

    -- Generate our string bytes and re-encode as a base64 string.
    key := encode(gen_random_bytes(6), 'base64');

    -- Base64 encoding contains 2 URL unsafe characters by default.
    -- The URL-safe version has these replacements.
    key := replace(key, '/', '_'); -- url safe replacement
    key := replace(key, '+', '-'); -- url safe replacement

    -- Concat the generated key (safely quoted) with the generated query
    -- and run it.
    -- SELECT id FROM "test" WHERE id='blahblah' INTO found
    -- Now "found" will be the duplicated id or NULL.
    EXECUTE qry || quote_literal(key) INTO found;

    -- Check to see if found is NULL.
    -- If we checked to see if found = NULL it would always be FALSE
    -- because (NULL = NULL) is always FALSE.
    IF found IS NULL THEN

      -- If we didn't find a collision then leave the LOOP.
      EXIT;
    END IF;

    -- We haven't EXITed yet, so return to the top of the LOOP
    -- and try again.
  END LOOP;

  -- NEW and OLD are available in TRIGGER PROCEDURES.
  -- NEW is the mutated row that will actually be INSERTed.
  -- We're replacing id, regardless of what it was before
  -- with our key variable.
  NEW.id = key;

  -- The RECORD returned here is what will actually be INSERTed,
  -- or what the next trigger will get if there is one.
  RETURN NEW;
END;
$$ language 'plpgsql';

我有一个已经包含数据的表，我添加了一个名为 pid 的新列是否可以修改它并使用函数调用作为默认值，以便我之前的所有数据都变得简短身份证号？

Answer 1

假设你有一个表test:

DROP TABLE IF EXISTS test;
CREATE TABLE test (foo text, bar int);
INSERT INTO test (foo, bar) VALUES ('A', 1), ('B', 2);

您可以向其中添加一个 id 列:

ALTER TABLE test ADD COLUMN id text;

并附加触发器:

DROP TRIGGER IF EXISTS unique_short_id_on_test ON test;
CREATE TRIGGER unique_short_id_on_test
    BEFORE INSERT ON test
    FOR EACH ROW EXECUTE PROCEDURE unique_short_id();

现在创建一个临时表，temp，具有与测试相同的结构(但没有数据):

DROP TABLE IF EXISTS temp;
CREATE TABLE temp (LIKE test INCLUDING ALL);
CREATE TRIGGER unique_short_id_on_temp
    BEFORE INSERT ON temp
    FOR EACH ROW EXECUTE PROCEDURE unique_short_id();

将 test 注入(inject) temp:

INSERT INTO temp (foo, bar)
SELECT foo, bar
FROM test
RETURNING *

产生类似的东西:

| foo        | bar | id       |
|------------+-----+----------|
| A          |   1 | 9yt9XQwm |
| B          |   2 | LCeiA-P8 |

如果其他表在 test 表上有外键引用，或者如果 test 必须保持在线，可能无法删除 test 并将 temp 重命名为 test。相反，使用 temp 中的 id 更新 test 会更安全。

假设test有一个主键(为了具体起见，我们称它为testid)，那么您可以使用 temp 中的 id 更新 test，使用:

UPDATE test
SET id = temp.id
FROM temp
WHERE test.testid = temp.testid;

然后你可以删除 temp 表:

DROP TABLE temp;