mysqli_multi_query: need to check single result? - php

Question

I'm using this code to insert a record with a unique id and then return the id-string just created:
$sql ="set #id=UUID();";
$sql .="INSERT INTO `items` (`id`,`parent`, `text`, `type`) VALUES(#id,'".$parent."', '".$text."', '".$type."');";
$sql .="select #id;";
if (mysqli_multi_query($conn, $sql)) {
while (mysqli_more_results($conn)) {
mysqli_use_result($conn);
mysqli_next_result($conn);
}//while
$result = array('id' => mysqli_store_result($conn)->fetch_row()[0]);
}//if
If everything works as it should, the three queries should return:
1/true (I guess)
1/true
object
I never used this function before and I was wondering: what happens if the insert query fails?
The third query will still be executed?
And in that case, how can I check the result of the second query?
Edit:
Or in general:
having a set of 10 queries, in case of failure how can I check which one has failed?

Answer 1

After some test...
Let's assume we have the following 3 queries:
$sql ="INSERT INTO `items` (`id`,`parent`) VALUES ('id',WRONG_NO_QUOTES);";
$sql .="INSERT INTO `items` (`id`,`parent`) VALUES ('id','right2');";
$sql .="INSERT INTO `items` (`id`,`parent`) VALUES ('id','right3');";
Using the code provided by the manual...
if (mysqli_multi_query($conn,$sql)) {
do {
/* store first result set */
if ($result = mysqli_store_result($conn)) {
while ($row = $result->fetch_row()) {
printf("%s\n", $row[0]);
}
$result->free();
}
/* print divider */
if (mysqli_more_results($conn)) {
printf("-----------------\n");
}
} while (mysqli_next_result($conn));
}
//...plus this....
if(mysqli_errno($conn)){
echo 'mysqli_errno:';
var_dump(mysqli_errno($conn));
echo'<br>';
}
...the output is:
mysqli_errno:
[...]test.php:39:int 1146
...and there are no changes to the database.
Conclusion:
When an error occours, the next queries are NOT executed.
AND the error can be easly catched at the end of the do/while loop.
EDIT
The code above generates a strict standards notice.
I edited it to avoid the notice and get a (basic) backtrace of the error:
$n=1;
$i=1;
if (mysqli_multi_query($conn,$sql)) {
do {
/* store first result set */
if ($result = mysqli_store_result($conn)) {
while ($row = $result->fetch_row()) {
echo $row[0];
}
$result->free();
}
/* print divider */
if (mysqli_more_results($conn)) {
echo "<hr>";
$n++;
mysqli_next_result($conn);
}else{$i=0;}
} while ($i>0);
}
if(mysqli_errno($conn)){
echo 'mysqli error on query number '.$n;
var_dump(mysqli_errno($conn));
}

Answer 2

Since my actual problem was to avoid competition between queries and get the right identifier (check: this question) I realized there is a simpler (and maybe better) way to reach the desired result (here using pdo extension):
$db = new PDO ("mysql:host=$hostname;dbname=$dbname", $user, $pass);
$db->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
//No user defined variable here inside (safe)
$identifier=db->query("SELECT UUID();")->fetch()[0];
Having the identifier stored into a PHP variable, then I can treat every following query separately using pdo and prepared statements.