Why Are My Database Row Counts Different Between Manual and PDO Execution?

Matching Rows in a Database: Troubleshooting Discrepancies

When attempting to determine row count to ascertain the presence of duplicate emails in a database, developers may encounter discrepancies between manual execution and execution via PDO execute. This issue arises from potential problems caused by both SQL errors and the data itself.

1. Addressing SQL Errors:

• Ensure that your query runs error-free. Refer to previous answers for guidance on diagnosing and resolving SQL errors.

2. Verifying Conditions:

• Check that your conditions are correct and not mutually exclusive. For instance, WHERE col=1 AND col=2 will not return any matches.

3. Debugging Data Issues:

• Verify that the involved variables exist and contain valid values.
• Inspect the input data for non-printable or encoded characters. These may prevent matches. Use rawurlencode() to make non-latin characters visible.

4. Connection Credential Problems:

• Confirm that you are connecting to the correct database. Check the database name in your connection credentials.

5. Character Set/Encoding Issues:

• Although rare, ensure correct character set and encoding settings by following the checklist provided in the referenced answer.

Case Study:

The issue described during email matching stemmed from encoded HTML entities in the email address. The query WHERE from_email = "abc Offers <[email protected]>" failed to match data containing "ab Offers &[email protected]".

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