Having issue with matching rows in the database

  Kiến thức lập trình

I am looking to get row count to check if same email is already in database or not. i have tried couple of mechanism but no success. when i run my query directly in the database it gives me the row count but via PDO execute it gives me 0.

i have used fetchAll method to manually count, even used rowCount method that also not working

$sql = 'SELECT count(*) FROM inbox WHERE uid = ? AND from_email = ?'; 
$result = $link->prepare($sql); 
$number_of_rows = $result->fetchColumn(); 

issue is with this $email_f, it contains html

SELECT count(*) FROM inbox WHERE uid = "6961" 
AND from_email = "abc Offers <[email protected]>"

this is the query which i have printed from $sql and when i execute it in database directly in phpmyadmin, it works fine. give me count of 3 but via execute i get 0.


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. So you need to investigate, why there is no match.

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.

In case the error says “no such table/database”, see the “connection credentials” case below.

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

First of all, in case a variable involved, make sure it exists and actually contains some value.

Then check the value itself. There could be some converted or non-printable characters in the input data (or database). For example 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 <[email protected]>. For a quick check you can use rawurlencode() function, it will convert all non-latin characters into codes, thus making them visible.

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


Theme wordpress giá rẻ Theme wordpress giá rẻ Thiết kế website