Question

通过下面的示例，我只使用表达式SIMILAR TO获得TRUE; LIKE和〜都显示为FALSE（我猜错了吗？）

由于SIMILAR TO在很多SO帖子中都不合适，我想通过使用LIKE或〜来了解是否有一种方法可以与正则表达式匹配。

students = ("James","John","Robert","Michael","William","David","Richard","Joseph","Thomas","Charles","Christopher","Daniel","Matthew","Anthony","Donald","Mark","Paul","Steven","Andrew","Kenneth","George","Joshua","Kevin","Brian","Edward","Mary","Patricia","Jennifer","Elizabeth","Linda","Barbara","Susan","Jessica","Margaret","Sarah","Karen","Nancy","Betty","Lisa","Dorothy","Sandra","Ashley","Kimberly","Donna","Carol","Michelle","Emily","Amanda","Helen","Melissa")
print("The gold medal goes to:",students[0])
print("The silver medal goes to:",students[1])
print("The bronze medal goes to:",students[2])
print("All winners in order:")
for index, student in enumerate(students in range(3,51)):
    place=str(index+1)
    print(place,student.title())

Answer 1

LIKE支持使用_对任何单个字符进行模式匹配，并为任何字符序列支持%，这样：

SELECT 'thomas' LIKE '%(h|x)%'

不起作用，因为LIKE不理解(...)进行分组或|进行更改，这些只是LIKE模式中的文字字符。

SIMILAR TO支持_和%与LIKE相同，但添加(...)分组，与|交替，以及其他一些内容，以便：

SELECT 'thomas' SIMILAR TO '%(h|x)%'

按预期工作。

~*使用POSIX正则表达式，因此(...)用于分组，|用于替换，但%只是百分号;这意味着：

SELECT 'thomas' ~* '%(h|x)%'

正在寻找被百分号包围的h或x，并且按预期方式无法正常工作。

如果您使用正确的正则表达式，则~*版本将起作用：

SELECT 'thomas' ~* '(h|x)' -- alternation
SELECT 'thomas' ~* 'h|x'   -- alternation without an unnecessary grouping
SELECT 'thomas' ~* '[hx]'  -- or a character class

上面链接的文档涵盖了所有这些内容。

Answer 2

在这种情况下你可以使用〜*：

SELECT 'thomas' ~* '.*(h|x).*'

或

SELECT 'thomas' ~* 'h|x'

请注意，您应该使用〜，〜*运算符使用POSIX正则表达式语法。

而不是LIKE和〜，为什么只有SIMILAR TO才能与正则表达式匹配替代品

2 个答案: