How do I Reference Capture Groups in MySQL Regular Expressions?

Referencing Capture Groups in MySQL Regex

When working with regular expressions in MySQL, it's essential to understand how to reference capture groups. Capture groups enable you to match and extract specific patterns within a string.

Problem: Unable to Reference Groups

In the question, the user attempts to capture a repeating character using the expression REGEXP '^(.)1$'. However, this attempt fails to reference the captured group correctly.

Solution

In MySQL 8 and beyond, you can reference capture groups using $1, $2, and so on. The following expression successfully captures and replaces a pattern:

SELECT REGEXP_REPLACE('stackoverflow','(.{5})(.*)','');
-- "overflowstack"

Here, (.{5}) captures a sequence of five characters, and (.*) captures any remaining characters. The result is a string with the captured groups interchanged: "overflowstack."

For MariaDB, capture group referencing uses \1, \2, etc.:

SELECT REGEXP_REPLACE('stackoverflow','(.{5})(.*)','\2\1');
-- "overflowstack"

Remember, capture groups allow you to target specific sections of a string, providing greater flexibility for pattern matching and manipulation in your MySQL queries.

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