Question

In my PHP code I have the following SQL statement:

$query = “UPDATE users SET num_logins = num_logins+1, last_login=’$timeStamp’ WHERE id = $id”;

I recently implemented the num_logins column for a project administrator so he could see who the frequent users are. It looks like it is working most of the time, however, I’ve noticed two users who have num_logins = 0 with timestamp values in the last_login field that fall after the date I implemented the change.

The default for the num_logins column is zero, so if they successfully login, and the above query is the only query that updates their last_login field, how is is that num_logins is still zero when their last_login field has been updated (neither field gets updated anywhere else in the code and I am the only db admin)?

ENGINE=InnoDB.

Answer 1

Some scenarios to consider:

1. Are you sure the $id is matching up properly on the update query? Maybe the record isn’t being updated.
2. Are you sure all values for the num_logins are not null? Is the column nullable? Default may be 0, but you should check to make sure there aren’t any null values. Remember, null + anything is always null.
3. Are you sure the query is actually being executed in your code? Can you add some instrumentation (e.g. logging) to ensure this? Maybe the query isn’t being run in all scenarios.