Error
Error Code:
2201B
PostgreSQL Error 2201B: Invalid Regular Expression
Description
PostgreSQL Error 2201B is a Data Exception indicating that a regular expression used in a query is syntactically incorrect or malformed. This error typically occurs during pattern matching operations (e.g., using `LIKE`, `SIMILAR TO`, or regex operators) when the provided regex pattern cannot be parsed by the database engine, preventing the query from executing.
Error Message
invalid regular expression
Known Causes
3 known causesMalformed Pattern Syntax
The regular expression pattern contains syntax errors, such as unclosed parentheses, brackets, or incorrect quantifier usage, making it unparsable.
Invalid Escape Sequences
The pattern uses escape sequences (e.g., `\d`, `\s`) that are either unsupported by PostgreSQL's regex engine or are incorrectly formed.
Character Encoding Issues
Characters within the regular expression pattern are not compatible with the database's or session's character encoding, leading to parsing failures.
Solutions
4 solutions available1. Review and Correct the Regular Expression Syntax easy
Identify and fix syntax errors in the problematic regular expression.
1
Locate the SQL query or function that is causing the 'invalid regular expression' error. This is often found in error logs or the application code interacting with PostgreSQL.
2
Carefully examine the regular expression string. Common syntax errors include: unescaped special characters (like `.`, `*`, `+`, `?`, `^`, `$`, `(`, `)`, `[`, `]`, `{`, `}`, `|`, `\`), incorrect character class definitions, or mismatched quantifiers.
3
Consult PostgreSQL's regular expression documentation (or standard POSIX ERE/BRE documentation if not using advanced features) to ensure correct syntax. For example, if you intend to match a literal dot, it must be escaped as `\.`. If you want to match a literal backslash, it must be escaped as `\\`.
4
Test the corrected regular expression using online regex testers or within a PostgreSQL session to confirm it functions as intended and no longer produces the error.
SELECT 'test string' ~ '^test\.$'; -- Example of a corrected regex2. Escape Special Characters in Dynamic SQL medium
Ensure special characters are properly escaped when constructing regular expressions dynamically.
1
If the regular expression is being built dynamically as a string within your application code (e.g., in Python, Java, PHP) or within PostgreSQL functions, ensure that any characters that have special meaning in regular expressions are properly escaped.
2
In SQL strings, a backslash `\` is used to escape characters. Therefore, to include a literal backslash in your regex string, you need to escape it twice: `\\`. To include a literal dot `.`, you'd use `\.`. To include a literal opening parenthesis `(`, you'd use `\(`.
-- Example: Constructing a regex to match a literal path like 'C:\Program Files\'3
For example, if your application needs to match a path like 'C:\Program Files\', and you are constructing the regex string in SQL, it should look like this:
sql
SELECT 'C:\Program Files\' ~ '^C:\\Program Files\\$' -- Escaping backslashes for regex
If the regex is generated from user input, sanitize and escape it rigorously.
sql
SELECT 'C:\Program Files\' ~ '^C:\\Program Files\\$' -- Escaping backslashes for regex
If the regex is generated from user input, sanitize and escape it rigorously.
SELECT 'path/to/file.txt' ~ '^path/to/file\.txt$'; -- Escaping the dot4
If using PostgreSQL's `quote_literal()` or `quote_nullable()` functions, be aware they are for SQL string literal escaping, not regex escaping. You will need to implement specific regex escaping logic.
3. Use PostgreSQL's `regexp_escape` Function easy
Leverage PostgreSQL's built-in function to automatically escape regex special characters.
1
If your regular expression needs to include literal occurrences of characters that have special meaning in regex (e.g., `.` `*` `+` `?` `|` `(` `)` `[` `]` `{` `}` `^` `$`), use the `regexp_escape()` function.
2
The `regexp_escape()` function takes a string and an optional flag. The default flag 'e' escapes characters for extended regular expressions (ERE).
SELECT regexp_escape('a.b*c?d');3
This function will return a string with all regex metacharacters escaped, ensuring they are treated as literal characters in your regex operation. Then, you can use this escaped string in your `~` or `~*` operator.
SELECT 'a.b*c?d' ~ regexp_escape('a.b*c?d'); -- This will always return true if the string contains 'a.b*c?d'4
This is particularly useful when the pattern for your regex comes from an external source or needs to match user-provided data literally.
4. Check for Incorrect Use of Basic vs. Extended Regular Expressions medium
Ensure the correct regex syntax is used based on whether you're using POSIX BRE or ERE.
1
PostgreSQL supports both POSIX Basic Regular Expressions (BRE) and Extended Regular Expressions (ERE). The `~` operator, by default, uses ERE. Some older or simpler regex implementations might expect BRE syntax.
2
In BRE, characters like `(`, `)`, `{`, `}`, `|`, `+`, and `?` do not have special meaning unless escaped. In ERE, they *do* have special meaning and must be escaped if you want to match them literally.
3
If you are inadvertently using BRE syntax with the `~` operator (which expects ERE), you will encounter errors. For example, `(abc)` is valid in BRE but needs to be `\(abc\)` in ERE to match the literal parentheses.
4
Review your regex and ensure it conforms to ERE syntax. If you specifically need BRE syntax, you might need to use a different operator or function, or carefully construct your ERE string to mimic BRE behavior by escaping where necessary for ERE.
-- Example of ERE syntax correctly used with '~'
SELECT 'Hello (World)' ~ 'Hello \(World\)';