MYSQL need help pulling data from each "user" using php - php

Question

Here's what I have. This code grabs the data from all of the users and subtracts 1 from user_days then updates every user's user_days row.
$result = mysqli_query($con,"SELECT * FROM users");
while($row = mysqli_fetch_array($result))
{
$minusone = $row['user_days']-1;
mysqli_query($con,"UPDATE users SET user_days=$minusone");
echo "<br />";
echo $row['user_days'];
}
The problem I'm having is this:
Instead of subtracting 1 from each user and updating each users field,
it's updating each user's field with the value from the first user.
example:
before updating
user 1 has 30 days
user 2 has 60 days
after updating
user 1 has 29 days
user 2 has 29 days (instead of 59 days)
Any help is appreciated and I hope this question is easy to understand.
Just to clarify, I DO want to update every field.
I just don't want the updates to be duplicated from the first result.
Thanks for all of the answers, this has given me a lot of help.

Answer 1

Why don't you just run UPDATE users SET user_days = user_days-1 WHERE id=XXXXX? And then select the whole thing?

Answer 2

When you update your record, you need to specify the user id for the record of interest, otherwise you current query updates all the rows in your table.

Answer 3

You should point which record to UPDATE
mysqli_query($con,"UPDATE users SET user_days=$minusone WHERE id=XXXXX");

Answer 4

The problem is with the UPDATE statement. Without a WHERE clause it will apply the SET clause to every row in the database. Assuming you have a unique id column named id in the users table, you could modify your code like this:
while($row = mysqli_fetch_array($result))
{
$minusone = $row['user_days']-1;
$user_id = $row['id'];
mysqli_query($con,"UPDATE users SET user_days=$minusone WHERE id=$user_id");
echo "<br />";
echo $row['user_days'];
}

Answer 5

Use the following Query:
mysqli_query($con,"UPDATE users SET user_days=$minusone WHERE user_ID = '".$row['user_ID']."'");

Answer 6

You're updating all the users with the same $minusone value. You need a WHERE clause in your update statement, like this:
$result = mysqli_query($con,"SELECT * FROM users");
while($row = mysqli_fetch_array($result))
{
$minusone = $row['user_days']-1;
$id_user = $row['id_user'];
mysqli_query($con,"UPDATE users SET user_days=$minusone WHERE id_user = $id_user");
echo "<br />";
echo $row['user_days'];
}
Another way of doing what you want would be:
...
$result = mysqli_query($con,"UPDATE users SET user_days = user_days - 1");
...
This assuming you want to substracts 1 to all user_days.

Answer 7

As already pointed out by other answers, the best way to do this is to replace your entire code block with one line.
mysqli_query($con, "UPDATE users SET user_days=user_days-1");
Then you can SELECT and display the information as needed.
Without knowing exactly what you are using user_days for, I'm thinking there may be a better approach to what you are trying to do. I am assuming this is some kind of subscription service, and this code will be run once per day to decrement the number of days to allow them to access the service.
A better approach would be to have a subscriptionExpires field in your database, which would hold a datetime value. Using your approach, if the job that runs this fails, every user will get an extra day. What if a web spider or a user finds your script, your users accounts will expire early. If you use an actual date for when the account expires, there's no guessing if the current value is correct.