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Description

This error occurs when a regular expression used in a MySQL function or statement contains a named capture group whose identifier does not conform to MySQL's required naming conventions. MySQL expects named capture groups to follow specific rules for identifiers, such as starting with an underscore or letter and containing only alphanumeric characters and underscores. It typically arises during the execution of queries involving REGEXP_ functions.

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Error Message

A capture group has an invalid name.

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Known Causes

3 known causes

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Disallowed Characters in Name

The named capture group contains characters (e.g., hyphens, spaces, or other special symbols) that are not permitted in MySQL identifiers.

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Name Starts with Number

The named capture group's identifier begins with a numeric character instead of a letter or underscore, which is invalid for MySQL identifiers.

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Reserved Keyword as Name

The chosen name for the capture group conflicts with a MySQL reserved keyword, leading to an invalid identifier.

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Solutions

3 solutions available

1. Correct Invalid Capture Group Names in REGEXP_REPLACE easy

Identify and rename invalid capture group names within REGEXP_REPLACE expressions.

1

Review your SQL queries that use the `REGEXP_REPLACE` function. Locate any instances where you've defined capture groups using `(?<name>...)` or `(name)` syntax.

SELECT REGEXP_REPLACE('some_string', 'pattern', 'replacement');

2

Ensure that capture group names adhere to MySQL's naming conventions: names must start with a letter and can contain letters, digits, and underscores. Avoid using reserved keywords or special characters in capture group names. If you are using unnamed capture groups (e.g., `(...)`), ensure they are correctly paired.

Example of an invalid name: `(?<1invalid>...)` or `(?<invalid-char>...)`
Example of a valid name: `(?<valid_name>...)` or `(?<validname1>...)`

3

Modify the `REGEXP_REPLACE` expression to use valid capture group names. For unnamed groups, simply ensure they are properly nested.

Original (potentially invalid): `SELECT REGEXP_REPLACE('abc123def', '(?<1digit>\d+)', 'X');`
Corrected: `SELECT REGEXP_REPLACE('abc123def', '(?<digits>\d+)', 'X');`

2. Simplify REGEXP_REPLACE to Avoid Named Capture Groups easy

If named capture groups are not essential, simplify the regex to use unnamed groups.

1

Examine your `REGEXP_REPLACE` statements. If the intent is to capture a part of the pattern and reuse it in the replacement string, but you don't need to refer to it by a specific name, consider using unnamed capture groups.

SELECT REGEXP_REPLACE('some_string', 'pattern_with_(capture)_group', 'replacement_using_\1');

2

Replace named capture groups `(?<name>...)` with simple parentheses `(...)`. Ensure that the backreferences in the replacement string (`\1`, `\2`, etc.) correctly correspond to the order of these unnamed capture groups.

Original (using named group): `SELECT REGEXP_REPLACE('abc123def', '(?<digits>\d+)', 'X');`
Simplified (using unnamed group): `SELECT REGEXP_REPLACE('abc123def', '(\d+)', 'X');`

3. Validate Regex Syntax and Capture Group Usage medium

Thoroughly test and validate the regular expression pattern and its capture group implementation.

1

Break down complex regular expressions into smaller, manageable parts. Test each part independently to ensure it matches as expected.

Use online regex testers (e.g., regex101.com) or MySQL's `REGEXP` operator for initial validation without affecting your data.

2

When using `REGEXP_REPLACE`, pay close attention to the syntax of capture groups. Ensure that all opening parentheses `(` have corresponding closing parentheses `)`. For named groups, verify the `?<name>` syntax is correct and the name follows MySQL's identifier rules.

Example: A regex like `(abc(def))` has two capture groups. The first captures `abcdef`, the second captures `def`. If you intended to name them, it would be `(?<first>abc(?<second>def))`.

3

If the error persists, consider simplifying the regex. Remove capture groups one by one to pinpoint which specific group is causing the invalid name issue. If you are using features not supported by the MySQL version you are on, consult the MySQL documentation.

Consult MySQL documentation for your specific version regarding `REGEXP_REPLACE` and its supported regex features.

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Related Errors

5 related errors

MySQL Error 3887: Invalid Capture Group Name