Determining whether mysql result is a valid resource

bunner_bob

I'm trying to do this:

 $result = mysql_query($query);
if (mysql_num_rows($result) > 0)
{
	// do stuff
}

The problem is, in some cases the query isn't returning anything. This is fine and expected, but mysql_num_rows($result) keeps giving me an error. I thought if I checked that the number of rows in the result was greater than 0, that would week out any results that didn't have rows, but apparently it isn't.

Is there a more appropriate check to see that a result really is a result before trying to do stuff with it?

laserlight

In such cases, the problem stems from one or more of these:
1. Failed to connect to database server.
2. Failed to select database.
3. Failed to execute SQL statement (e.g., syntax error, mismatch of column names).

Returning an empty result set is not an error of this sort.

NogDog

First check to see if $result === false. If it does, then the query failed in one of the ways LL mentioned, above. You can then log an error with info from mysql_error(), the actual query string, etc. to help debug (but don't display that stuff to the user on a live system!).

If it is not false, then you can do your num_rows check and anything else you want to do with the result set.

bunner_bob

Ahh - that was it. I thought I was just getting an empty result. There was an out-of-range unix date that was tripping things up.

I usually use a nice database abstraction layer - so much that I've more or less forgotten how to write "real" sql queries 🙂