如果此查询失败，如何使用mysqli_rollback

Question

I am trying to use mysqli_rollback() when a query fails. This nested sub-query should return null as 'qwerty' does not exist. However, no exception message is generated?

<?php
$con = mysqli_connect("x","y","z","zz");

// Check connection
if (mysqli_connect_errno()) {
    echo "Failed to connect to MySQL: " . mysqli_connect_error();
}

try {
    mysqli_autocommit($con,FALSE);

    mysqli_query($con,"INSERT INTO customer (id, name, mobile) values ((select id from somewhere where something = 'qwerty'), 'john', '01234567890')");
    mysqli_commit($con);

} catch (Exception $e) {
  echo 'Message: ' .$e->getMessage();

  mysqli_rollback($con);
}

?>

CREATE customer table given below:

CREATE table customer
(
id int NOT NULL,
name varchar(100) NOT NULL,
mobile varchar(100),
PRIMARY KEY (id)
);

Answer 1

the query isn't causing an error, so there is nothing to catch.

$sql = 'select ....';
$result=$con->query($sql);
$count = $con->affected_rows;
if($count<0){do something because this is an error};
else if($count==0){do something when nothing inserted};
else {do something to tell me record was inserted};