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Description

This error indicates that a regular expression function or operator in MySQL, such as `REGEXP` or `RLIKE`, was called with an argument that is syntactically incorrect, malformed, or of an inappropriate data type. It typically occurs when the provided regular expression pattern itself is invalid or when a non-string value is supplied where a string pattern is expected.

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Error Message

Illegal argument to a regular expression.

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Known Causes

3 known causes

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Invalid Regex Pattern Syntax

The regular expression string provided contains syntax errors, unmatched parentheses, or invalid escape sequences, making it unparsable by the MySQL regex engine.

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Non-String Regex Argument

A non-string value (e.g., a number, a boolean, or an unexpected data type) was passed as the regular expression pattern where a string is explicitly required.

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Empty or NULL Pattern

An empty string or NULL value was supplied as the regular expression pattern, which the regex engine considers an illegal argument in the given context.

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Solutions

4 solutions available

1. Escape Special Characters in Regex easy

Ensure all characters with special meaning in regular expressions are properly escaped.

1

Identify the regular expression pattern used in your MySQL query.

2

For characters that have special meaning in regular expressions (e.g., ., ^, $, *, +, ?, (, ), [, ], {, }, |, \), prepend them with a backslash (\) to treat them as literal characters.

UPDATE your_table SET your_column = 'new_value' WHERE your_column REGEXP '^some\.pattern\*$'

3

Re-run your query with the escaped regular expression.

2. Simplify the Regular Expression medium

Break down complex regex patterns into simpler, valid components.

1

Examine your regular expression for excessive nesting, overly complex character classes, or ambiguous quantifiers.

2

If possible, rewrite the regex to achieve the same matching logic with simpler constructs. For instance, instead of complex lookarounds or nested groups, consider alternative approaches.

Consider replacing `(a|b)+` with `a+b+|ab+` if the intent is to match one or more 'a's followed by one or more 'b's, or vice versa, if applicable.

3

Test the simplified regex in a regex tester tool or within MySQL to ensure it still matches your intended data.

4

Apply the simplified regex to your MySQL query.

SELECT * FROM your_table WHERE your_column REGEXP 'simplified_pattern'

3. Use Alternative String Matching Functions easy

Employ LIKE or SOUNDEX if regex is not strictly necessary.

1

Determine if the exact functionality of a regular expression is required. For simple pattern matching (e.g., wildcards), the `LIKE` operator is often sufficient and more performant.

2

If you need to match based on phonetic similarity, consider using the `SOUNDEX` function.

3

Rewrite your query using `LIKE` or `SOUNDEX` if they meet your requirements.

SELECT * FROM your_table WHERE your_column LIKE '%partial_string%';

4

Alternatively, for phonetic matching:

SELECT * FROM your_table WHERE SOUNDEX(your_column) = SOUNDEX('target_word');

4. Update MySQL Server to a Newer Version advanced

Older MySQL versions might have bugs or limitations in their regex engine.

1

Check your current MySQL server version using the following command:

SELECT VERSION();

2

Consult the MySQL documentation for the regex capabilities and any known issues in your current version.

3

If your version is significantly old, plan and execute a MySQL upgrade to a supported and more recent version. This is a more involved process and requires careful planning, backups, and testing.

4

After upgrading, re-test your queries with the regular expressions.

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Related Errors

5 related errors

MySQL Error 3685: Illegal Regular Expression Argument