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Description

Error 3852 indicates a problem with the regular expression pattern or its application within a MySQL function. This server-side error occurs when the database engine encounters invalid syntax, an unsupported feature, or an unparseable pattern in a regex-related function like `REGEXP_LIKE`, `REGEXP_REPLACE`, or `REGEXP_INSTR`.

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Error Message

Regex error: %s in function %s.

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Known Causes

4 known causes

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Invalid Regular Expression Syntax

The regular expression pattern used in the query contains syntax errors, such as unescaped special characters, mismatched parentheses, or incorrect quantifiers.

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Unsupported Regex Feature

The regular expression pattern includes advanced features or constructs (e.g., lookaheads/lookbehinds, specific Unicode properties) that are not supported by MySQL's regex engine.

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Incorrect Function Arguments or Flags

The regex function (e.g., `REGEXP_LIKE`) is called with an invalid number of arguments, incorrect data types, or unsupported flag options, leading to a parsing error.

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Character Encoding Mismatch

The regular expression pattern contains characters that are not compatible with the column's or database's character set and collation, causing the regex engine to fail.

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Solutions

3 solutions available

1. Correcting Invalid Regular Expression Syntax easy

Identify and fix the specific syntax error in your REGEXP or RLIKE expression.

1

Examine the error message carefully. The `%s` placeholder in the error message will typically contain the specific regex syntax error (e.g., 'unmatched parenthesis', 'invalid character range').

MySQL Error 3852: Regex error: unmatched parenthesis in function REGEXP.

2

Locate the SQL query that is causing the error. This is usually a `SELECT`, `UPDATE`, or `DELETE` statement using `REGEXP` or `RLIKE` in a `WHERE` clause.

SELECT * FROM your_table WHERE your_column REGEXP 'your_invalid_regex';

3

Consult the MySQL documentation for valid regular expression syntax. Common mistakes include unescaped special characters (like `.` , `*`, `+`, `?`, `(`, `)`, `[`, `]`, `{`, `}`, `|`, `^`, `$`) and incorrect character class definitions.

Refer to: https://dev.mysql.com/doc/refman/8.0/en/regexp.html

4

Rewrite the regular expression to conform to valid syntax. For example, if you intended to match a literal dot, escape it with a backslash.

Incorrect: 'your.regex'
Correct: 'your\.regex'

5

Test the corrected query to ensure it executes without the error.

SELECT * FROM your_table WHERE your_column REGEXP 'your_corrected_regex';

2. Escaping Special Characters in Regular Expressions medium

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

1

Identify if your regular expression contains characters that have special meaning in regex syntax. These include: `.` `^` `$` `*` `+` `?` `(` `)` `[` `]` `{` `}` `|` `\`.

Example: You want to match the literal string '192.168.1.1'. Without escaping, '.' would match any character.

2

Prepend a backslash (`\`) before each special character you want to treat as a literal character.

To match '192.168.1.1' literally, use: '192\.168\.1\.1'

3

If you need to match a literal backslash, you must escape it with another backslash: `\\`.

To match a literal backslash, use: '\\'

4

Apply the corrected, escaped regex to your SQL query.

SELECT * FROM logs WHERE ip_address REGEXP '192\.168\.1\.1';

3. Simplifying Complex or Incorrect Regex Patterns medium

If the regex is overly complex or fundamentally flawed, simplify or rebuild it.

1

Understand the exact pattern you are trying to match. Break down the requirement into smaller, manageable parts.

Requirement: Match email addresses with a specific domain like 'example.com'.

2

If the current regex is very long and difficult to parse, consider if there's a simpler way to achieve the same result. Sometimes, using string functions alongside or instead of regex can be more readable and less error-prone.

Instead of a complex regex for email: `SELECT * FROM users WHERE email REGEXP '^[a-zA-Z0-9._%+-]+@example\.com$'`
Consider a simpler approach if just checking domain: `SELECT * FROM users WHERE email LIKE '%@example.com'` (though this is less strict).

3

If rebuilding, start with basic anchors (`^` for start, `$` for end) and then add character sets and quantifiers as needed. Test each component of the regex incrementally.

To match a simple email format:
1. Start: `^`
2. Username part: `[a-zA-Z0-9._%+-]+`
3. '@' symbol: `@`
4. Domain part: `example\.com`
5. End: `$`
Combined: `^[a-zA-Z0-9._%+-]+@example\.com$`

4

Ensure you are using the correct regex flavor. MySQL uses a subset of POSIX Extended Regular Expressions.

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Related Errors

5 related errors

MySQL Error 3852: Invalid Regex Syntax