regex - 使用 postgres 正则表达式捕获一个点

Question

我有这些字符串:

3           FD160497.   2016  abcd
3           FD160497   2016  abcd

我想捕获“FD”、数字，然后是点(如果存在)。

我试过这个:

SELECT
    sqn[1] AS letters,
    sqn[2] AS digits,
    sqn[3] AS dot
FROM (
    SELECT
        regexp_matches(string, '.*?(FD)([0-9]{6})(\.)?.*') as sqn
    FROM
        mytable
) t;

(PostgreSQL 9.5.3)

“点”列在这两种情况下都是 NULL，我真的不知道为什么。 它适用于 regex101 .

Answer 1

第一个懒惰模式使当前分支中的所有量词都懒惰，所以你的模式等价于

.*?(FD)([0-9]{6})(\.)??.*?
                     ^^  ^

查看其 demo at regex101.com

参见 9.7.3.1. Regular Expression Details excerpt :

...matching is done in such a way that the branch, or whole RE, matches the longest or shortest possible substring as a whole. Once the length of the entire match is determined, the part of it that matches any particular subexpression is determined on the basis of the greediness attribute of that subexpression, with subexpressions starting earlier in the RE taking priority over ones starting later.

您需要在一个分支中始终如一地使用量词:

regexp_matches(string, '.*(FD)([0-9]{6})(\.)?.*') as sqn

或

regexp_matches(string, '.*[[:blank:]](FD)([0-9]{6})(\.)?.*') as sqn

参见 regex demo