How to fix 2200S: invalid_xml_comment in PostgreSQL

First, locate the XML comment causing the error. Check your XML data for comment sections starting with <!-- and ending with -->. Look for:
1. Comments containing -- within the text
2. Comments missing the closing -->
3. Malformed comment syntax

You can use PostgreSQL's xml_is_well_formed_document() function to test your XML:

SELECT xml_is_well_formed_document('<!-- Valid comment --><root/>');
SELECT xml_is_well_formed_document('<!-- Invalid -- comment --><root/>');

XML comments cannot contain double hyphens (--) anywhere within the comment text. This is a strict XML specification rule. If your comments contain --, you must:
1. Remove the double hyphens
2. Replace with single hyphens or other characters
3. Use CDATA sections for content that needs --

Example of problematic comment:

<!-- This is -- invalid -->

Corrected version:

<!-- This is - invalid -->

Verify all comments are properly closed with -->. Common issues include:
1. Missing closing tag: <!-- Comment only
2. Extra hyphens: <!-- Comment --->
3. Wrong delimiter: <!-- Comment ->

Use an XML validator or text editor with XML syntax highlighting to identify unclosed comments. PostgreSQL's XML parser is strict about comment closure.

Depending on your needs:
1. Remove unnecessary comments: If comments are not essential, strip them from your XML data
2. Fix syntax errors: Ensure all <!-- ... --> constructs are properly formed
3. Replace -- sequences: Change double hyphens to single hyphens or other separators
4. Use CDATA sections: For content that might contain problematic sequences

For application-generated XML, ensure your XML generation library properly handles comment syntax.

After making corrections, test your XML data:

-- Test with valid comment
SELECT xmlparse(document '<!-- Single hyphen comment --><root/>');

-- Test with your actual data
SELECT xml_is_well_formed_document(your_xml_data);

-- If using xml columns
INSERT INTO xml_table (xml_data) VALUES ('<!-- Valid --><data/>');

Ensure all comments follow XML syntax rules before attempting to parse or store the data.

If you're importing XML from external sources:
1. Implement XML validation before processing
2. Use PostgreSQL's xml_is_well_formed_document() as a guard
3. Consider stripping comments if they're not needed
4. Use XML transformation to fix comment syntax

Example validation pattern:

WITH xml_input AS (
  SELECT '<!-- External data --><root/>' as xml_text
)
SELECT 
  CASE WHEN xml_is_well_formed_document(xml_text) 
    THEN xmlparse(document xml_text)
    ELSE NULL
  END as parsed_xml
FROM xml_input;