Why Do My Database Row Counts Differ Between Direct Queries and PDO Results?

Troubleshooting Row Matching Discrepancies in the Database

Encountering discrepancies between row counts obtained directly from the database and those returned through PDO can be frustrating. Let's delve into the potential issues and provide a systematic approach to debugging.

Database Conditions

First, verify that the SQL query executes without errors. A simple error could result in no rows being returned. Check for mutually exclusive conditions in your WHERE clause that could prevent matches.

Data-Related Issues

Variables involved in the query should be present and contain valid values. Inspect the values carefully for special characters or symbols that may interfere with the match. HTML entities like < or > can cause unexpected issues. Consider using rawurlencode() to uncover non-Latin characters.

Connection Authenticity

Ensure you're connecting to the correct database containing the data you're seeking. If you manage multiple databases, double-check the connection credentials.

Character Set/Encoding

Rarely, character set or encoding issues can affect row matching. Examine your database and input data using the checklist from this resource: [Great Character Encoding Answer](https://stackoverflow.com/questions/18342462/encoding-problem-between-mysql-and-php).

Debug Process

1. Enable full error reporting for both PDO and PHP to reveal potential errors.
2. Scrutinize the database data and input for disparities, using rawurlencode() to expose hidden characters.
3. Verify that you're connected to the intended database with the correct credentials.
4. Investigate character set and encoding issues if all else fails.

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