正则表达式（所有在第一场比赛之后（没有第一场比赛））

Question

I am struggling with the easy Regex expression. Basically I want everything after the first match of "_" without the "_".

My current expression is like this: _(.*)

When I give input: AAA_BBB_CCC

The output is: _BBB_CCC

My ideal output would be: BBB_CCC

I am using a snowflake database with their build-in regex function.

Unfortunately, I can not use (?<=_).* as it does not support this format of "?<=". Is there some other way how can I modify _(.*) to get the right output?

Thank you.

Answer 1

You can use a regular expression to achieve this, something like this is JavaScript for example will do the job

"AAA_BBB_CCC".replace(/[^_]+./, '')

Use REGEXP_REPLACE with Snowflake

regexp_replace('AAA_BBB_CCC','^[^_]+_','')

https://docs.snowflake.net/manuals/sql-reference/functions/regexp_replace.html

But you can also find the first index of _ and use substring, available in all languages

let text = "AAA_BBB_CCC"
let index = text.indexOf('_')
if(index !== -1 && index < text.length) {
    let result = text.substring(index+1)
}

Answer 2

In Snowflake SQL, you may use REGEXP_SUBSTR , its syntax is

REGEXP_SUBSTR( <string> , <pattern> [ , <position> [ , <occurrence> [ , <regex_parameters> [ , <group_num ] ] ] ] ) .

The function allows you to return captured substrings :

By default, REGEXP_SUBSTR returns the entire matching part of the subject. However, if the e (for “extract”) parameter is specified, REGEXP_SUBSTR returns the the part of the subject that matches the first group in the pattern. If e is specified but a group_num is not also specified, then the group_num defaults to 1 (the first group). If there is no sub-expression in the pattern, REGEXP_SUBSTR behaves as if e was not set.

So, you need to set the regex_parameters to e and - optionally - group_num argument to 1 :

Select REGEXP_SUBSTR('AAA_BBB_CCC', '_(.*)', 1, 1, 'e', 1)
Select REGEXP_SUBSTR('AAA_BBB_CCC', '_(.*)', 1, 1, 'e')

Answer 3

Use a capture group:

\_(?<data>.*)

Which returns the capture group data containing BBB_CCC

Example: https://regex101.com/r/xZaXKR/1

Answer 4

To get this actually working you need to use:

SELECT REGEXP_SUBSTR('AAA_BBB_CCC', '_(.*)', 1, 1, 'e', 1);

which gives:

REGEXP_SUBSTR('AAA_BBB_CCC', '_(.*)', 1, 1, 'E', 1)
BBB_CCC

you need to pass the REGEXP_SUBSTR parameter <regex_parameters> clause of e as that is extract sub-matches. thus Wiktor's answer is 95% correct.