Why Does My PDO Query Return 0 Rows While the Direct SQL Query Returns the Correct Count?

Row Matching Discrepancy between Database Query and PDO Execution

While attempting to check for duplicate email addresses in a database, a developer encounters a discrepancy between direct database query execution and execution through a PDO prepared statement.

The Issue

When executing a query via PDO to count rows with a specific email address, the result returns 0, despite similar queries executed directly in the database returning the correct row count.

Potential Causes

SQL Errors:

• Validate that the query runs without errors that may prevent data retrieval. Refer to PDO and MySQL resources for handling errors.

Condition Errors:

• Ensure that the conditions used in the query are accurate and mutually exclusive to avoid empty results. Simplify conditions to ensure data retrieval before refining them.

Data Discrepancies:

• Verify that the email address variable used in the query exists and contains a value.
• Check for unusual characters or HTML entities in the email address, as they may disrupt matching. Use rawurlencode() to expose hidden characters.

Connection Credentials:

• Confirm that the PDO connection is established to the correct database containing the expected data.

Character Set/Encoding:

• Ensure that the character set and encoding used in the database and PDO connection match to prevent encoding issues that may affect result accuracy.

Example Issue

The provided code snippet includes an email address that contains HTML entities, potentially causing the discrepancy:

$email_f = "abc Offers <[email&#160;protected]>";

Conclusion

Addressing these potential causes by debugging PDO issues, scrutinizing input data, checking connection credentials, and verifying character set compatibility can help resolve discrepancies between database query and PDO execution.

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