将值从基数N中的字符串表示转换为数字

Question

在我的数据库中,我将特定表示法中的数字保存为varchar值.有没有办法用选定的表示法将这些值强制转换为小数？

我在这里看起来应该是这样的:

SELECT to_integer_with_notation('d', '20')

 int4
 ---------
 13

还有一个例子:

SELECT to_integer_with_notation('d3', '23')

 int4
 ---------
 302

Answer 1

不幸的是,在PostgreSQL中没有内置函数,但可以写得相当简单:

CREATE OR REPLACE FUNCTION number_from_base(num TEXT, base INTEGER)
  RETURNS NUMERIC
  LANGUAGE sql
  IMMUTABLE
  STRICT
AS $function$
SELECT sum(exp * cn)
FROM (
  SELECT base::NUMERIC ^ (row_number() OVER () - 1) exp,
         CASE
           WHEN ch BETWEEN '0' AND '9' THEN ascii(ch) - ascii('0')
           WHEN ch BETWEEN 'a' AND 'z' THEN 10 + ascii(ch) - ascii('a')
         END cn
  FROM regexp_split_to_table(reverse(lower(num)), '') ch(ch)
) sub
$function$;

注意:我用作numeric返回类型,int4在许多情况下是不够的(使用更长的字符串输入).

编辑:这是一个反向函数示例,它可以将bigint自定义库中的文本表示转换为:

CREATE OR REPLACE FUNCTION number_to_base(num BIGINT, base INTEGER)
  RETURNS TEXT
  LANGUAGE sql
  IMMUTABLE
  STRICT
AS $function$
WITH RECURSIVE n(i, n, r) AS (
    SELECT -1, num, 0
  UNION ALL
    SELECT i + 1, n / base, (n % base)::INT
    FROM n
    WHERE n > 0
)
SELECT string_agg(ch, '')
FROM (
  SELECT CASE
           WHEN r BETWEEN 0 AND 9 THEN r::TEXT
           WHEN r BETWEEN 10 AND 35 THEN chr(ascii('a') + r - 10)
           ELSE '%'
         END ch
  FROM n
  WHERE i >= 0
  ORDER BY i DESC
) ch
$function$;

用法示例:

SELECT number_to_base(1248, 36);

-- +----------------+
-- | number_to_base |
-- +----------------+
-- | yo             |
-- +----------------+