Notice warning appears when formatting timestamp field in PHP. How to solve it?

Question

You can see that the correct results are output, but a warning appears. How to solve it?

code show as below:

Answer 1

It turns out that what is taken out seems to be in time format, but is actually a string. Use strtotime() to solve the problem.

The code is posted below:

$dataMonth=date('m',strtotime($row['creation time'])) ;