PHP - Error handling while querying mysql - php

Question

I am new to web development, so probably there is something I am doing it wrong.
I am using webmatrix for development and playing around with StarterSite sample that webmatrix provides.
In one of the php file (header.php) there is a query to mysql using mysqli extension. I have changed the tablename to some non existent table to simulate error condition. The problem is, after below statement -
$statement->execute();
the script stops.
I inserted a echo statement after execute and that echo string is not displaying on webpage. However when I correct the table name, the echo string after execute is displayed on webpage. So I think the script stops executing after execute when the table name is wrong. I have two questions. How do I stop script from stop executing like this? Secondly How to know for sure that script has stopped executing at some particular statement?
For second part of question, I checked the log file and tracelog file in IISExpress folder. There is no mention of any error, probably because error happened in MYSQL. However, in my MYSQL folder there is no log file, so not sure how to check mysql log.
If I have missed anything, please let me know.
Regards,
Tushar

Answer 1

You should read about mysqli error handling.
Basic error handling example OOP:
if ($mysqli->connect_errno) {
printf("Connect failed: %s\n", $mysqli->connect_error);
exit();
}
Procedural:
if (mysqli_connect_errno()) {
printf("Connect failed: %s\n", mysqli_connect_error());
exit();
}

Answer 2

It depends on what you're logging. In the error log you can define what's being logged. I think you can control the strict mode of the error in the php.ini which will automatically throw error into the access_log or error_log or apache log file.
The trick is to use $mysqli->error in every step of the mysqli querying and db connects to ensure you're getting proper error messages in detail whether to debug, improve the code or to do it correctly.
Here is an example of using $mysqli->error in querying the database.
$result = $mysqli->query($query);
if (!$result and $mysqliDebug) {
// the query failed and debugging is enabled
echo "<p>There was an error in query: $query</p>";
echo $mysqli->error; //additional error
}
You can also use a method where you define mysql error to be true in db conn
// define a variable to switch on/off error messages
$mysqliDebug = true;
// connect to your database
// if you use a single database, passing it will simplify your queries
$mysqli = #new mysqli('localhost', 'myuser', 'mypassword', 'mydatabase');
// mysqli->connect_errno will return zero if successful
if ($mysqli->connect_errno) {
echo '<p>There was an error connecting to the database!</p>';
if ($mysqliDebug) {
// mysqli->connect_error returns the latest error message,
// hopefully clarifying the problem
// NOTE: supported as of PHP 5.2.9
echo $mysqli->connect_error;
}
// since there is no database connection your queries will fail,
// quit processing
die();
}
#ref: https://www.daniweb.com/web-development/php/code/434480/using-phpmysqli-with-error-checking