Thursday, March 22, 2018

php - Why can't I run two mysqli queries? The second one fails




Is it possible to have two mysqli queries like so?



mysqli_query($dblink, "INSERT INTO images (project_id, user_id, image_name, date_created, link_to_file, link_to_thumbnail, given_name) VALUES ('$project_id', '$user_id', '$image_name', '$date_created', '$link_to_file', '$thumbnail', '$ImageName')");
mysqli_query($dblink, "INSERT INTO images_history (project_id, user_id, image_name, date_created, link_to_file, link_to_thumbnail, given_name, day, month, year) VALUES ('$project_id', '$user_id', '$image_name', '$date_created', '$link_to_file', '$thumbnail', '$ImageName', '$day', '$month', '$year')");



Basically I want to update two tables in my DB. Is there a better way to do this?


Answer



It is possible with mysqli_multi_query().



Example:





$mysqli = new mysqli($host, $user, $password, $database);

// create string of queries separated by ;
$query = "INSERT INTO images (project_id, user_id, image_name, date_created, link_to_file, link_to_thumbnail, given_name) VALUES ('$project_id', '$user_id', '$image_name', '$date_created', '$link_to_file', '$thumbnail', '$ImageName');";
$query .= "INSERT INTO images_history (project_id, user_id, image_name, date_created, link_to_file, link_to_thumbnail, given_name, day, month, year) VALUES ('$project_id', '$user_id', '$image_name', '$date_created', '$link_to_file', '$thumbnail', '$ImageName', '$day', '$month', '$year');";

// execute query - $result is false if the first query failed
$result = mysqli_multi_query($mysqli, $query);

if ($result) {

do {
// grab the result of the next query
if (($result = mysqli_store_result($mysqli)) === false && mysqli_error($mysqli) != '') {
echo "Query failed: " . mysqli_error($mysqli);
}
} while (mysqli_more_results($mysqli) && mysqli_next_result($mysqli)); // while there are more results
} else {
echo "First query failed..." . mysqli_error($mysqli);
}



The key is that you must use mysqli_multi_query if you want to execute more than one query in a single call. For security reasons, mysqli_query will not execute multiple queries to prevent SQL injections.



Also keep in mind the behavior of mysqli_store_result. It returns FALSE if the query has no result set (which INSERT queries do not) so you must also check mysqli_error to see that it returns an empty string meaning the INSERT was successful.



See:
mysqli_multi_query
mysqli_more_results
mysqli_next_result
mysqli_store_result


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