Is there a difference between mysqli_num_rows and select count(*)

Question

Sometimes I would like to get the amount of results in a query, often I use mysqli_num_rows to do that, example:

$count = mysqli_query($this->db,"SELECT * FROM `test`");
return mysqli_num_rows($count);

With count:

$count = mysqli_query($this->db, "SELECT COUNT(*) as cnt FROM test");
$row = mysqli_fetch_assoc($count);
return $row['cnt'];

Is there any difference between these two ways to get the number of rows returned?

score 4 · Answer 1 · answered Aug 16 '16 at 16:03

4

Yes.

The former one should never be used, because it will select all the table data from database and send it to PHP, choking server in the process.

While the latter one is selecting and sending a single number.

answered Aug 16 '16 at 16:03

Your Common Sense

Ok, so the second one is faster in terms of speed. – Piqka Aug 16 '16 at 16:03
@Piqka Not only faster; it's also safer. If you try to use `mysqli_num_rows()` with a big table, you may crash your server – Barranka Aug 16 '16 at 17:36

1 Answers1