Maybe the title is not that clear but assume this situation:
I have a form to update a specific row of a table. When I submit the form an UPDATE query is performed.
I count the number of affected rows to determine if the query went right or not.
$row->execute();
$count = $row->rowCount();
if($count==0){
http_response_code(500);
}else{
http_response_code(200);
}
This works well if the user submit the form by changing any data. If the form is left unchanged the query will affect 0 results and my code will return 500.
But the point is that the query was properly executed.
So my question is: is there a way mysql will tell me that 0 row where affected because nothing changed in the data instead of any other case (eg. wrong value in a field or so on?). So that my if can become something like this:
if($count==0||$no_field_changed==false){
Gordon already gave you the answer in his comment,
You should check the error conditions to see if the query succeeded
but just to make it obvious I will expand upon it for you.
$status = $row->execute();
if ( ! $status ) {
// the query errored
$arr = $row->errorInfo();
error_log(print_r($arr,1), 3, 'db_error.log'));
http_response_code(500);
exit;
}
// So if we get here the query ran successfully
if($row->rowCount() == 0){
// Nothing was changed by our query this time but it ran successfully
http_response_code(200);
}else{
// Something was changed by our query
http_response_code(200);
}
Related
I have a table in my DB which I just added a new column to, and when I query this table in Perl I want to check only once if this field is empty or not. I need to check the value of this column in just the first row. Usually to go through the query results I use
while (my $row = $sthmm->fetchrow_hashref()) {
# do stuff
}
I could check each row in the while loop but since I only need to do it once, I don't want to waste time doing that.
How can I retrieve one row and check the column's value without consuming it, meaning that I can still go through the whole result in the while loop after checking this condition.
if ( my $row = $sth->fetchrow_hashref() ) {
# Do stuff with first row
do {
# Do stuff to be done to each row
} while $row = $sth->fetchrow_hashref();
}
I'd like to check if value entered in the php form already exist in MySQL database, and show message if same value is found, and ofc different message if no duplicate was found.
I used this code:
$result = $conn->query("SELECT id FROM tb_cform WHERE u_email = '".$_POST['u_email']."'");
if($result->num_rows == 0) {
echo'Mail address was not forund in database!';
} else {
die("Mail address already exist in the database!");
}
However, i keep getting the "else" part of the statement whatever email I enter, so I always get "Mail address already exist in the database!" message.
Any help please?
Oh, got it, I placed the whole code at the wrong place in file, it was placed after I actually run a query for adding the email in the database, and therefore check always returned that mail is found, my mistake, sorry!
I am using below code to get records with specified condition, and then to update only the same records.
$this->db->where('Parameter1', 'TRUE');
$query = $this->db->get('Messages');
$this->db->where('Parameter1', 'TRUE');
$this->db->set('Parameter1', 'FALSE');
$this->db->update('Messages');
This works, but calling two times the same query using where() command seems like wasting of server power. Is it possible to make get() command not reset query or to use the previous record set in the update command?
I doubt this is something you really need to worry about taking up too many resources, and you can't really reuse the where clause in the actual sql query. But if you'd like you can refactor to get slightly cleaner code.
$unread = array('Parameter1'=>TRUE);
$read = array('Parameter1'=> FALSE);
$query = $this->db->get_where('Messages', $unread);
$this->db->update('Messages', $read, $unread);
Note:
In your code your getting every element where Parameter1 is set to true, and then changing every one of those elements to false. This almost certainly is not desirable, but perhaps it is a problem you take care of somewhere else in your real application.
I'm writing a simple forum for a php site. I'm trying to calculate the post counts for each category. Now a category can belong to another category with root categories being defined as having a NULL parent_category_id. With this architecture a category can have an unlimited number of sub-categories and keeps the table structure fairly simple.
To keep things simple lets say the categories table has 3 fields: category_id, parent_category_id, post_count. I don't think the remaining database structure is relevant so I'll leave it out for now.
Another trigger is calling the categories table causing this trigger to run. What I want is it to update the post count and then recursively go through each parent category increasing that post count.
DELIMITER $$
CREATE TRIGGER trg_update_category_category_post_count BEFORE UPDATE ON categories FOR EACH ROW
BEGIN
IF OLD.post_count != NEW.post_count THEN
IF OLD.post_count < NEW.post_count THEN
UPDATE categories SET post_count = post_count + 1 WHERE categories.category_id = NEW.parent_category_id;
ELSEIF OLD.post_count > NEW.post_count THEN
UPDATE categories SET post_count = post_count - 1 WHERE categories.category_id = NEW.parent_category_id;
END IF;
END IF;
END $$
DELIMITER ;
The error I'm getting is:
#1442 - Can't update table 'categories' in stored function/trigger because it is already used by statement which invoked this stored function/trigger.
I figure you can do a count() on each page load to calculate the total posts but on large forums this will slow things down as discussed many times on here (e.g. Count posts with php or store in database). Therefore for future proofing i'm storing the post count in the table. To go one step further I thought i'd use triggers to update these counts rather than PHP.
I understand there are limitations in MySQL for running triggers on the same table that's being updated which is what is causing this error (i.e. to stop an infinite loop) but in this case surely the loop would stop once it reaches a category with a NULL parent_category_id? There must be some kind of solution whether it's adjusting this trigger or something different entirely. Thanks.
EDIT I appreciate this might not be the best way of doing things but it is the best thing I can think of. I suppose if you changed a parents category to another it would mess things up, but this could be fixed by another trigger which re-syncs everything. I'm open to other suggestions on how to solve this problem.
I usually recommend against using triggers unless you really, really need to; recursive triggers are a great way of introducing bugs that are really hard to reproduce, and require developers to understand the side effects of an apparently simple action - "all I did was insert a record into the categories table, and now the whole database has locked up". I've seen this happen several times - nobody did anything wrong or stupid, it's just a risk you run with side effects.
So, I would only resort to triggers once you can prove you need to; rather than relying on the opinion of strangers based on generalities, I'd rig up a test environment, drop in a few million test records, and try to optimize the "calculate posts on page load" solution so it works.
A database design that might help with that is Joe Celko's "nested set" schema - this takes a while to get your head round, but can be very fast for querying.
Only once you know you have a problem that you really can't solve other than by pre-computing the post count would I consider a trigger-based approach. I'd separate out the "post counts" into a separate table; that keeps your design a little cleaner, and should get round the recursive trigger issue.
The easiest solution is to fetch all the posts per category and afterwards link them together using a script/programming language:
for instance in php:
<?php
// category: id, parent, name
// posts: id, title, message
$sql = "select *, count(posts.id) From category left join posts ON posts.cat = category.id Group by category.id";
$query = mysql_query($sql);
$result = array();
while($row = mysql_fetch_assoc($query)){
$parent = $row['parent'] == null ? 0 : $row['parent'];
$result[$parent][] = $row;
}
recur_count(0);
var_dump($result);
function recur_count($depth){
global $result;
var_dump($result[$depth],$depth);
foreach($result[$depth] as $id => $o){
$count = $o['count'];
if(isset($result[$o['id']])){
$result[$depth][$id]['count'] += recur_count($o['id']);
}
}
return $count;
}
Ok so for anyone wondering how I solved this I used a mixture of both triggers and PHP.
Instead of getting each category to update it's parent, I've left it to the following structure: a post updates it's thread and then a thread updates it's category with the post count.
I've then used PHP to pull all categories from the database and loop through adding up each post count value using something like this:
function recursiveCategoryCount($categories)
{
$count = $categories['category']->post_count;
if(!is_null($categories['children']))
foreach($categories['children'] as $child)
$count += recursiveCategoryCount($child);
return $count;
}
At worst instead of PHP adding up every post on every page load, it only adds up the total category posts (depending at what node in the tree you are in). This should be very efficient as you're reducing the total calculations from 1000s to 10s or 100s depending on your number of categories. I would also recommend running a script every week to recalculate the post counts in case they become out of sync, much like phpBB. If I run into issues using triggers then I'll move that functionality into the code. Thanks for everyones suggestions.
I am currently getting products from one site, storing them in a database, and then having their prices display on another site. I am trying to get the prices from the one site to update daily in my database so the new updated prices can be displayed onto my other site.
Right now I am getting the products using an item number but have to manually go in and update any prices that have changed.
I am guessing I am going to have to use some kind of cronjob but not sure how to do this. I have no experience with cronjobs and am a noob with php.
Any ideas?
Thanks!
I have done some reading on the foreach loop and have written some code. But my foreach loop is only running once for the first item number. The foreach loop runs then goes to the "api.php" page but then stops. It doesn't continually loop for each item number. How do I tell it to go through all of item numbers in my database?
Also if you see anything else wrong in my code please let me know.
Thanks
....
$itemnumber = array("".$result['item_number']."");
foreach ($itemnumber as $item_number) {
echo "<form method=\"post\" action=\"api.php\" name=\"ChangeSubmit\" id=\"ChangeSubmit\">";
echo "<input type=\"text\" name=\"item_number\" value=\"{$item_number}\" />";
echo "<script type=\"text/javascript\">
function myfunc () {
var frm = document.getElementById(\"ChangeSubmit\");
frm.submit();
}
window.onload = myfunc;
</script></form>";
}
}
If you already retrieve the product data from an external site and store it in a local database, updating the prices from the same source should be no problem to you. Just retrieve the data, iterate through it in a foreach loop or similar and update the prices to the database based on the item number.
Once you have created the update script and run it manually, adding it as a cronjob will be as simple as running the command `crontab -e´ and adding this row to execute your script every midnight:
0 0 * * * /usr/local/bin/php /path/to/your/script.php
Don't forget to use the correct path for PHP for your system, running which php in the shell will tell you the path.
If you have cronjob's on your server, it'll be very apparent- You make a PHP script that updates it, and throw it in a daily cronjob.
However, I do it this way:
Method 1: At the beginning of every page request, check the last "update" time (you choose how to store it). If it's been more than a day, do the update and set the "update" time to the current time.
This way, every time someone loads a page and it's been a day since the last update, it updates for them. However, this means it's slower for random users, once a day. If this isn't acceptable, there's a little change:
Method 2: If you need to update (via the above method of checking), start an asyncronous request for the data, handle the rest of the page, flush it to the user, then in a while loop wait until the request finishes and update it.
The downside to method 2 is that the user won't see the updated values, but, the benefit is that it won't be any more of a wait for them.