始终会影响MySQL中的行

Question

In PHP, I'm using mysqli_affected_rows to validate whether a user has been registered in a database, where a query looks something like this:

"UPDATE schedule WHERE userid = '$user' AND date='2018-05-05'"

If the user doesn't exist, the number of affected rows is 0, and if they do exist, it's 1.

This works OK, except for when a user is registered in a second time. Here, MySQL will say 0 rows are affected, since there has been no change to the schedule.

Is there anything I can add to my query to always affect rows? Or is this just a poor approach?

Answer 1

To check whether a user exists in a database, I would use a select statement instead.

sql = "SELECT * FROM schedule WHERE userid = '$user' AND date='2018-05-05'"

Then do something if a user exists

$result = $conn->query($sql);
if ($result->num_rows > 0) {
//user exists 
}

I would also assume you would like to have unique users in the database? I that case I would check whether a user exists first using the same code before adding a new record.