在plpgsql中生成唯一的随机字符串 [英] Generate unique random strings in plpgsql
问题描述
我正在尝试编写一个函数来创建可变长度的唯一随机令牌.但是,我对plpgsql语法感到困惑.我的意图是创建一个功能
I am trying to write a function to create unique random tokens of variable length. However, I am stumped by the plpgsql syntax. My intention is to create a function which
- 将表和列作为输入
- 生成具有给定字符集的给定长度的随机字符串
- 检查字符串是否已经在列中
- 如果是这样(预计这种情况很少见),只需生成一个新的随机字符串.
- 否则,返回随机字符串
我当前的尝试如下:
CREATE FUNCTION random_token(_table TEXT, _column TEXT, _length INTEGER) RETURNS text AS $$
DECLARE
alphanum CONSTANT text := 'abcdefghijkmnopqrstuvwxyz23456789';
range_head CONSTANT integer := 25;
range_tail CONSTANT integer := 33;
random_string text;
BEGIN
REPEAT
SELECT substring(alphanum from trunc(random() * range_head + 1)::integer for 1) ||
array_to_string(array_agg(substring(alphanum from trunc(random() * range_tail + 1)::integer for 1)), '')
INTO random_string FROM generate_series(1, _length - 1);
UNTIL random_string NOT IN FORMAT('SELECT %I FROM %I WHERE %I = random_string;', _column, _table, _column)
END REPEAT;
RETURN random_string;
END
$$ LANGUAGE plpgsql;
但是,这不起作用,并且给了我一个不太有用的错误:
However, this doesn't work, and gives me a not very helpful error:
DatabaseError:错误'ERROR:"REPEAT"或附近的语法错误
DatabaseError: error 'ERROR: syntax error at or near "REPEAT"
我尝试了多种变体,但不知道语法中的错误是什么,我感到很困惑.知道如何解决此功能吗?
I have tried a number of variations, but without knowing what the error in the syntax is I am stumped. Any idea how to fix this function?
推荐答案
plpgsql中没有repeat
语句.使用简单的 loop
.
There is no repeat
statement in plpgsql. Use simple loop
.
CREATE OR REPLACE FUNCTION random_token(_table TEXT, _column TEXT, _length INTEGER) RETURNS text AS $$
DECLARE
alphanum CONSTANT text := 'abcdefghijkmnopqrstuvwxyz23456789';
range_head CONSTANT integer := 25;
range_tail CONSTANT integer := 33;
random_string text;
ct int;
BEGIN
LOOP
SELECT substring(alphanum from trunc(random() * range_head + 1)::integer for 1) ||
array_to_string(array_agg(substring(alphanum from trunc(random() * range_tail + 1)::integer for 1)), '')
INTO random_string FROM generate_series(1, _length - 1);
EXECUTE FORMAT('SELECT count(*) FROM %I WHERE %I = %L', _table, _column, random_string) INTO ct;
EXIT WHEN ct = 0;
END LOOP;
RETURN random_string;
END
$$ LANGUAGE plpgsql;
请注意,random_string
应该是format()
的参数.
Note, random_string
should be a parameter to format()
.
更新.根据Abelisto的准确提示,对于大桌子,这应该更快:
Update. According to the accurate hint from Abelisto, this should be faster for a large table:
DECLARE
dup boolean;
...
EXECUTE FORMAT('SELECT EXISTS(SELECT 1 FROM %I WHERE %I = %L)', _table, _column, random_string) INTO dup;
EXIT WHEN NOT dup;
...
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