Having issue with matching rows in the database using PDO

by

When there is no match it means there is no match. No matter what you think. When your query returns no rows, then there is no rows to match the condition.

Problems caused by SQL errors

First of all you need to make sure that your query actually runs without errors as “no result” could mean there was an error in your query.

Problems caused by the condition

Check your conditions. There are mutual exclusive conditions, such as WHERE col=1 AND col=2. It will never return any rows, Try to simplify the condition until it starts returning some rows, and then refine the conditions to get the desired result.

But even if you can swear there is data in the table to match your query, there are some pitfalls:

Problems caused by the data

Most likely there are some converted or non-printable characters in the input data (or database). For example, there could be a linefeed character or a peculiarly encoded symbol, or some characters such as < and > converted into HTML entities. As a result, the query contains <[email protected]> will never match a text &lt;[email protected]&gt;.

The problem is, this is only a guess, and nobody can tell you what the actual issue is, because it is your database, your input data and only you can find the issue.

I wrote an article that explains how to debug your PDO issues.

To debug a particular issue, you need

  • make sure the full error reporting is enabled for both PDO and PHP. It really helps, showing you occasional typographic errors, spelling errors and the such
  • scrutinize both the data in the database and the input to find the difference. bin2hex() function would help, revealing all non-printable and converted characters, in both database and the input.

Problems caused by the connection credentials

Another frequent issue is when you have several databases and connect to the wrong one that doesn’t have the data requested. This issue is similar to this one, so just follow the same routine, only checking not the list of tables but the data rows.

An irrelevant but important note

On a side note, but very important nevertheless: your prepared statement is a cargo cult code that protects nothing. Here is how it must be:

$sql="SELECT count(*) FROM inbox WHERE uid = ? AND from_email = ?"; 
$result = $link->prepare($sql); 
$result->execute([$email_number,$email_f]); 
$number_of_rows = $result->fetchColumn();

More Related Contents:

  1. PDOException SQLSTATE[HY000] [2002] No such file or directory
  2. PHP PDO: charset, set names?
  3. How to get numeric types from MySQL using PDO?
  4. How can I use PDO to fetch a results array in PHP?
  5. Causes of MySQL error 2014 Cannot execute queries while other unbuffered queries are active
  6. mysql PDO how to bind LIKE
  7. Use bound parameter multiple times
  8. What is the difference between MySQL, MySQLi and PDO? [closed]
  9. how safe are PDO prepared statements
  10. Can I use a PDO prepared statement to bind an identifier (a table or field name) or a syntax keyword?
  11. PHP PDO – Num Rows
  12. How to solve General error: 2006 MySQL server has gone away
  13. How to install pdo driver in php docker image?
  14. Replacing mysql_* functions with PDO and prepared statements
  15. MySQL retrieve variable from Stored Procedure in PHP PDO
  16. Understanding pdo mysql transactions
  17. Calling stored procedure with Out parameter using PDO
  18. When *not* to use prepared statements?
  19. How to insert an array into a single MySQL Prepared statement w/ PHP and PDO
  20. Setting a connect timeout with PDO
  21. In PHP with PDO, how to check the final SQL parametrized query? [duplicate]
  22. What is the best way to insert multiple rows in PHP PDO MYSQL?
  23. PDO MySQL: Insert multiple rows in one query
  24. How to bind LIKE values using the PDO extension?
  25. Error while using PDO prepared statements and LIMIT in query [duplicate]
  26. PDO prepared statement fetch() returning double results
  27. Warning: PDO::__construct(): [2002] No such file or directory (trying to connect via unix:///tmp/mysql.sock) in
  28. SQLSTATE[HY093]: Invalid parameter number: parameter was not defined
  29. PHP 7 RC3: How to install missing MySQL PDO
  30. Is a BLOB converted using the current/default charset in MySQL?

Leave a Comment