从不同的表PHP返回数组

I want to create an function to fetch data from different tables which have different table. Is it possible?

This is my function code

<?php
// Check connection

function fetch_data($selectsql){
include 'connectdb.php';
$result = $conn->query($selectsql);
if($result->num_rows <= 0 ){
echo "0 results";
}
else{
while ($row = $result->fetch_assoc()){  
return $row = array();
}
}
}
?>

and this is for use testing my function

<?php
include 'fetch_data_test.php';
include 'connectdb.php';

$selectsql = "SELECT * FROM user";
$row = fetch_data($selectsql);
echo $name = $row["name"];
echo $lastname = $row["lastname"];
$conn->close();


?>

but it didn't work. Can someone help me? or explain me more about how it can get and array.

Error:

Notice: Undefined index: name in /var/www/html/home/use_fetch.php on line 7 
Notice: Undefined index: lastname in /var/www/html/home/use_fetch.php on line 8

First you are return empty array for your function fetch_data. . Return you data outside your while loop

<?php
// Check connection

function fetch_data($selectsql){
 $rows=array();// create an array
include 'connectdb.php';
$result = $conn->query($selectsql);
if($result->num_rows <= 0 ){
echo "0 results";
}
else{
while ($row = $result->fetch_assoc()){  
      $rows= $row;// assign your data to array
}
}
return $rows;// return array
}
?>

Second you have to assign your return values form function to variable

<?php
include 'fetch_data_test.php';
include 'connectdb.php'

$selectsql = "SELECT * FROM user";
$row=fetch_data($selectsql);// assing into a variable
echo $name = $row["name"];
echo $lastname = $row["lastname"];
$conn->close();


?>

You're returning a blank array when you use this code return $row = array(); You need to fix that.

Also, you're not saving returned value to any variable.

In your code to test your function, change fetch_data($selectsql); to $rows = fetch_data($selectsql);

        <?php
        // Check connection

        function fetch_data($selectsql){

        include 'connectdb.php';
        $rows = array();        
        $result = $conn->query($selectsql);
        if($result->num_rows <= 0 ){
            echo "0 results";

        } else{
            while ($row = $result->fetch_assoc()){  
                  $rows[] = $row;
            }
        }

        $conn->close();
        return $rows;

        }

        ?>

        <?php
        include 'fetch_data_test.php';

        $selectsql = "SELECT * FROM user";
        $rows = fetch_data($selectsql);
        foreach($rows as $row){
            echo $name = $row["name"];
            echo $lastname = $row["lastname"];
            echo "
";
        }


        ?>