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Question

whereas the "users" table does not exist, catch be executed, the "errors" function is executed

Code :

<?php

$usuario = 'root';

$senha ='';

function errors($e)
{
    echo "Erro dados";
}

set_exception_handler('errors');

try
{

    $conn1 = new PDO('mysql:host=localhost;dbname=teste',$usuario, $senha);

}

catch(Exception $e){

    echo 'Erro ao conectar com o banco';

    die();  
}

try
{

    $sql= "SELECT * FROM usuarios";

    $resul = $conn1->query($sql);

    $resul = $resul->fetch(PDO::FETCH_ASSOC);

    foreach ($resul as $key => $value) {
        echo $key .": ". $value. "</br>";   
    }
}catch(Exception $e)
{

echo "Erro ao selecionar dados";

    die();

}

Answer 1

Basically, an Exception is not being released. When your query is executed, it does not return a Resultset, which makes it impossible to call the fetch function. With this PHP launches a type of error called E_NOTICE, which is not an instance of the Exception class.

Anyway the only way (more or less) to catch the run is to launch an Exception manually inside the Try. Something like this:

throw new Exception("Erro na consulta sql");

Example for the second Try/catch to work:

try
{
    $sql= "SELECT * FROM usuarios";
    $resul = $conn1->query($sql);

    //quando a query sql falhar, por qualquer motivo, 
    //será retornado o boolean false.
    if($resul === false){
        throw new Exception("Erro na consulta sql, algum campo não existe");    
    }
    $resul = $resul->fetch(PDO::FETCH_ASSOC);

    foreach ($resul as $key => $value) {
    echo $key .": ". $value. "</br>";   
    }
}catch(Exception $e)
{

    echo "Erro ao selecionar dados: " . $e->getMessage();
        die();

}

In this case your set_exception_handler will no longer run in this specific situation.