如何从 SELECT 查询中获取行数？ 错误：mysqli_affected_rows() 期望参数 1 是 mysqli，给定的对象

Question

I am working on making server side validation for a form. Using AJAX, the form sends the value in the input field for 'username' to my php page which then checks to see if this username already exists in the database.

Here is my php code:

$result = mysqli_query($dblink, "SELECT * FROM users WHERE `username` = '$regname'") 
or die(mysqli_error($dblink));
echo mysqli_affected_rows($result);

*(At the moment I am doing a simple echo for the mysqli_affected_rows just to see if my MySQL query is working as intended)*

The error I am getting is:

Warning: mysqli_affected_rows() expects parameter 1 to be mysqli, object given in /Users/test/Sites/proj/formvalidate.php on line 20

I am not quite sure what this error is trying to tell me. From what I have Googled "object" is a reference to OOP programming methods, but (as far as I know) I am not using OOP concepts/principles in this particular example? Or did I misinterpret this error message?

Thank you.

Answer 1

Rather than passing $result in to mysqli_affected_rows you actually want to pass the DB link (returned by mysqli_connect ) which will give you the number of rows affected by the previous query. See:

http://uk.php.net/mysqli_affected_rows

Answer 2

echo mysqli_affected_rows($dblink);

The mysqli object contains the count of the affected rows not the result set. I recommend you to use mysqli with OO style or try PDO.

Answer 3

You want to the number of the selected rows.

mysqli::$affected_rows should be used for INSERT, UPDATE, REPLACE or DELETE queries (affected_rows PHP.net) .

For SELECT queries (what you want) there is mysqli_result::$num_rows (num_rows PHP.net) . As you see num_rows should be used on the result from the SELECT query.

What you want is echo mysqli_num_rows ( $result ) which gives you the number of the selected rows.

An example for the usage from both of them:

$mysqli = new mysqli("localhost", "my_user", "my_password", "world");

$mysqli->query("CREATE TABLE Language SELECT * from CountryLanguage");
echo "Affected rows (INSERT): " . $mysqli->affected_rows; // $mysqli is the link variable to the DB

$result = $mysqli->query("SELECT Code, Name FROM Country ORDER BY Name");
echo "Selected rows: " . $result->num_rows; // Here we use the $result variable from the query

Answer 4

您应该只提供$mysqli_link （在您的情况下$dblink ），而不是您编写的代码中的$result 。

Answer 5

echo mysqli_num_rows($result);

这应该有效。