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The PHP documentation contains the reasons why an affected_rows statement might return 0, 1, -1 or even 3 in some scenarios, as does the answer to this particular stack question.

PHP / MySQLI: strange readings for affected_rows

But the wall I hit was that affected_rows was returning NULL. I did not find any stack question which currently answers this issue. So I figured out why it would return NULL.

Its because you are making a mistake in your syntax. I tend to associate the usage of affected_rows to the same as num_rows. But in fact the usage of both is different and that is why I got the particular NULL value.

num_rows usage:

$query = $handler->query("some select query");
$rows = $query->num_rows;

this would return the proper number of rows;

affected_rows usage:

$query = $handler->query("some update insert query");
$rows = $query->affected_rows;

this would return null as the $query variable unlike the previous $query would return true or false. Therefore in such a case you would always have to make calls to the $handler database connector object.

This is a problem I dealt with just now and now when I go back and look at the docs page I see that I've totally missed it. I think many people tend to treat affected_rows the same way as num_rows, but that's just me. But I think even though the question is a self-answering one it deserves a place here, because it took me almost 12 hours before I finally did a var_dump and got to the core of the issue.

If someone knows a better answer to this then please improve this answer.

The question lies in why are both num_rows and affected_rows treated differently in such a context?

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Koustav Pal
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  • have you tried `$handler->affected_rows;`? – ɹɐqʞɐ zoɹǝɟ Apr 30 '14 at 02:56
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    So, where is the question? – sectus Apr 30 '14 at 02:57
  • yes, a var_dump revealed that $query returns boolean, i finally solved the issue then because it makes sense that it will return NULL when called from a non-object bool var. I would have posted this as an answer but it seems this question hasn't been asked before. – Koustav Pal Apr 30 '14 at 03:00
  • If you want to post an answer to a question that has not been asked, you will need to first ask a question. The form that you just used to post this is called "Ask Question" - that's the first step you need to take. I think you might not have enough reputation to [ask and answer your own question](http://stackoverflow.com/help/self-answer) - in which case, try answering other questions to gain the reputation needed (15 rep), then come back and post your answer. – BoltClock Apr 30 '14 at 09:37

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