How Can You Reference Captured Groups in MySQL Regular Expressions?

Capture Group Referencing in MySQL Regular Expressions

When working with regular expressions in MySQL, capturing groups can be used to extract portions of text. However, unlike many other programming languages, MySQL does not provide the same level of support for referring to captured groups in subsequent regex substitutions.

In MySQL 8, the REGEXP_REPLACE function introduces the ability to reference capture groups using $1, $2, etc. For example, the following query replaces the first five characters of the string 'stackoverflow' with the remaining characters:

<code class="sql">SELECT REGEXP_REPLACE('stackoverflow','(.{5})(.*)',''); -- "overflowstack"</code>

MariaDB also allows capturing in REGEXP_REPLACE, but references are made using 1, 2, etc.

However, it is important to note that in earlier versions of MySQL, such as MySQL 5.7 and prior, there was no direct support for referencing capture groups in regular expressions. In these versions, techniques such as replacing the entire match with a literal string, or using Perl-compatible regular expressions (PCRE) through the external PCRE library, were necessary to reference captured groups.

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