How to diagnose and fix the 2201B invalid_regular_expression error code in Postgres.

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The 2201B: invalid_regular_expression error in PostgreSQL indicates that there is a syntax error in a regular expression used in a query. This error typically occurs when the regular expression pattern is not written correctly according to the syntax rules that PostgreSQL expects.

To diagnose and fix this error, follow these steps:

  1. Review the Regular Expression: Look at the regular expression pattern in your query and check for any syntax errors. Common mistakes include unbalanced brackets, parentheses, or braces, and unescaped special characters.
  2. Check for Unescaped Characters: Special characters like ., *, +, ?, |, ^, $, (, ), [, ], {, }, and \ should be escaped with a backslash (\) if you want to use them as literal characters in the pattern.
  3. Balance Brackets and Parentheses: Make sure that all opening brackets, parentheses, and braces have a corresponding closing counterpart.
  4. Use Correct Quantifiers: Ensure that quantifiers like *, +, and ? are used correctly and have valid operands.
  5. Test the Regular Expression: You can test the regular expression outside of PostgreSQL using a regular expression testing tool to ensure that it is valid and behaves as expected.

Here are some examples of how the 2201B error might occur and how to resolve it:

  • Unescaped Special Character:
  SELECT 'text' ~ '.*[.].*';

This will result in an error because the . inside the brackets is a special character that should be escaped. To fix it, escape the .:

  SELECT 'text' ~ '.*[\.].*';
  • Unbalanced Brackets:
  SELECT 'text' ~ '[abc';

This will cause an error due to the unbalanced brackets. To resolve it, close the brackets:

  SELECT 'text' ~ '[abc]';
  • Invalid Quantifier:
  SELECT 'text' ~ 'a{2,1}';

This will result in an error because the quantifier {2,1} is invalid (the minimum can’t be greater than the maximum). To fix it, use a valid quantifier:

  SELECT 'text' ~ 'a{1,2}';

For more detailed information on PostgreSQL regular expressions and error codes, you can refer to the PostgreSQL documentation on pattern matching. When encountering the 2201B error, carefully reviewing and correcting the regular expression in your query is typically the best approach.

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