Extract Substring Using Regular Expression: A POSIX BRE Solution

A comprehensive guide to extracting substrings using Regular Expressions in Snowflake POSIX BRE without lookbehind and lookahead features. Learn with real examples!
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Extracting Substrings Using Regular Expressions in Snowflake POSIX BRE

In the world of data manipulation, Regular Expressions (Regex) are invaluable tools for searching, matching, and manipulating text. However, when working with the Snowflake cloud data platform using the POSIX Basic Regular Expressions (BRE) engine, developers often encounter challenges due to the limitations of not supporting lookahead and lookbehind assertions. This guide aims to solve the problem of extracting substrings from given text while adhering to these constraints.

The Problem Explained

You might find yourself needing to extract specific substrings from strings that follow a particular format. For instance, take the following examples:

Input: 2022 CKL04 TER-PRO:CPT-REFRESH PRD|NPR
Required Output: CPT-REFRESH PRD

Input: 2022 CA4A TER-PRO:CPT-REFRESH PRD
Required Output: CPT-REFRESH PRD

Input: 2022 CDDR4A TER-PRO:CPT-LEASING PRD|MC|LQPRI13
Required Output: CPT-LEASING PRD

Input: 2022 CAP04A TER-PRO:PRODUCT|NPR
Required Output: PRODUCT

Input: 2022 CS040 TER-PRO:MS-PRD & SVC ANNUAL|NPR
Required Output: MS-PRD & SVC ANNUAL

In all these examples, the goal is to extract the substring that appears after the colon (:) and before either the first pipe (|) or the end of the string if no pipe exists.

The Solution: POSIX BRE Regex Pattern

Since the POSIX BRE doesn’t allow lookbehind or lookahead, we need to use a different approach. Here’s a breakdown of the regex pattern that can achieve the extraction:

Regex Pattern Used:

[[See Video to Reveal this Text or Code Snippet]]

Explanation of the Pattern:

regexp_substr: The function that is used to extract the substring we want.

col: This is the name of your column containing the string from which you want to extract the substring.

':': The pattern starts by looking for the character :. This defines where the extraction should begin.

([^|]+ ): This part defines a capturing group. It will match one or more characters [^|] that are not a pipe (|).

1, 1: These argument values specify to start searching from the first character and return the first match.

'e': This flag is used when you want the regex to act on the expression right after the colon.

The logic behind this approach is straightforward: start at the colon, and keep capturing everything that follows until you either hit the pipe or the end of the string.

Conclusion

Extracting substrings using Regular Expressions in the Snowflake POSIX BRE environment may seem daunting, especially without features like lookbehind and lookahead. However, by using the regex pattern outlined above, you can effectively achieve your goal of substring extraction seamlessly.

By following this method, you will find it much easier to deal with similar challenges while parsing strings in your Snowflake database.

If you have more complex scenarios or additional questions, feel free to reach out, and happy regex crafting!