Having issue with matching rows in the database

✔ Recommended Answer

First of all, you have to embrace the fact: if your query found no rows, it means there is no match, even if you can swear the data is all right. When the query returns no rows, then there are no rows to match the condition. So you have to find out - why. But first of all you need to make sure that your query is all right:

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 an error in the query. Refer to these answers for the details: pdo and mysqli.

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 all right, there are no errors, conditions are correct, and you can swear there is data in the table to match your query. Still, 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 <abc@abcs.com> will never match a text &lt;abc@abcs.com&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. urlencode() 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.

Problems caused by character set/encoding

It's a rare case, but just to to be sure, follow the checklist from this great answer

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();
 It's possible that the issue you are experiencing is related to the way you are executing your PDO query. Here are a few things you can check:

  1. Make sure that you are using the correct SQL syntax for your query. Double-check that the query you are executing in PDO is the same as the query you are running directly in the database.

  2. Check that the PDO connection is working properly. You can try executing a simple query like SELECT 1 to see if you get any results.

  3. Verify that the email value you are searching for is correct and has the same format as the email values in the database. Make sure that there are no leading or trailing spaces, for example.

  4. Check that the PDO fetch mode is set correctly. If you are trying to get a row count, you should use the PDO::FETCH_COLUMN fetch mode to get the result as a single value.

Here is an example of how you could execute a query to get a row count using PDO:


php
$email = 'test@example.com';
$stmt = $pdo->prepare('SELECT COUNT(*) FROM users WHERE email = :email');
$stmt->execute(['email' => $email]);
$count = $stmt->fetch(PDO::FETCH_COLUMN);


 In this example, we are using a prepared statement to execute the query and passing the email value as a parameter. We then use the fetch method with the PDO::FETCH_COLUMN fetch mode to get the row count as a single value.

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