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What value is returned from an empty sql query?

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What value is returned from an empty sql query?

Feb 26th, 2009

Sorry been out of commision for a few months.
Got a newbe question.

What value is returned from an sql query that returns no rows?

Example:

 Help with Code Tags 
 php Syntax (Toggle Plain Text) 
$a = "SELECT * FROM a WHERE b = c";
$b = my_sql_query($a);
$a = "SELECT * FROM a WHERE b = c";
$b = my_sql_query($a);

Note:
Table Name - a
Table Field - b
Table Field Value - c

Question:
In the table there is no value of c and hence nothing is returned
What is the value of $b?

Thanks, Regards X

PS: I am assuming 0 or NULL but nothing seems to be working, thanks.

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Re: What value is returned from an empty sql query?

Feb 26th, 2009

Then if you do mysql_num_rows($b) it will return 0 and if you attempt to fetch an array from the query then mysql will throw an error. So the value of b is still the query execute command but it just won't execute and instead will throw an error.

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Re: What value is returned from an empty sql query?

Feb 26th, 2009

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In the table there is no value of c and hence nothing is returned
What is the value of $b?

$b will still hold a result resource. Check Return values here..
http://in.php.net/function.mysql-query

Last edited by nav33n; Feb 26th, 2009 at 4:52 am.

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Re: What value is returned from an empty sql query?

Feb 26th, 2009

I dont think that is correct because when I make the variable that holds the result == 0 / NULL it dosent work.

How could you demonstrate that:

 Help with Code Tags 
 php Syntax (Toggle Plain Text) 
$a = "SELECT * FROM a WHERE b = c";
$b = mysql_query($a);
if($b == 0) {
 echo "No rows retrieved";
} else {
 echo "Rows retrieved";
}
$a = "SELECT * FROM a WHERE b = c";
$b = mysql_query($a);
if($b == 0) {
 echo "No rows retrieved";
} else {
 echo "Rows retrieved";
}

So anything something like this possible?

THanks, Regards X

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Re: What value is returned from an empty sql query?

Feb 26th, 2009

You have to get the number of rows.

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 php Syntax (Toggle Plain Text) 
$a = "SELECT * FROM a WHERE b = c";
$b = mysql_query($a);
$num_rows = mysql_num_rows($b);
if($num_rows == 0) {
 echo "No rows retrieved";
} else {
 echo "Rows retrieved";
}
$a = "SELECT * FROM a WHERE b = c";
$b = mysql_query($a);
$num_rows = mysql_num_rows($b);
if($num_rows == 0) {
 echo "No rows retrieved";
} else {
 echo "Rows retrieved";
}

Is that what you were asking?

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Re: What value is returned from an empty sql query?

Feb 26th, 2009

Your skipping a step

Because you cant preform num_rows if $b returns no rows and throws an error.
Been trying to come up with a solution but it is annoying me - hopefully I figure it out soon

Last edited by OmniX; Feb 26th, 2009 at 11:42 pm.

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Re: What value is returned from an empty sql query?

Feb 26th, 2009

Actually, I modified your query to test the code in my db prior to posting and it outputted "No rows retrieved'". Also, when I run the code like so:

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 php Syntax (Toggle Plain Text) 
$sql = 'SELECT * FROM `absent faculty table` WHERE absentid = "blah"'; 
$result=mysql_query($sql,$conn);
$num_rows = mysql_num_rows($result);
echo $num_rows;
$sql = 'SELECT * FROM `absent faculty table` WHERE absentid = "blah"'; 
$result=mysql_query($sql,$conn);
$num_rows = mysql_num_rows($result);
echo $num_rows;

it returns 0 every time.

Have you got an error in your query?

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Re: What value is returned from an empty sql query?

Feb 26th, 2009

You got it all wrong. $b doesn't return any rows. It just return result resource, which can be used in
* mysql_num_rows to know how many rows were returned.
* mysql_fetch_array/mysql_fetch_assoc/mysql_fetch_row/mysql_fetch_object to get the values of the rows .

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Re: What value is returned from an empty sql query?

Feb 26th, 2009

nav33n is correct it is returning a result resouce (but I was meaning to say if that result resource returns no rows).

buddylee17 that returned 0 always? Intresting... My query works because when it does "retrieve a row" there is no error but when "dosent retrieve a row" there is an error

Anyways to check if the result_resource contains "no rows" so then dosent throw an error?

Hmmm... Actually I think I know what may be the problem I think because I am calling the mysql_num_rows from a function then directly?

Ill bbs, after I have tinkered. Thanks for the input.

Ya solved it in .5 seconds with your help, ha (the function was causing the errors).

Thanks Guys

 Help with Code Tags 
 php Syntax (Toggle Plain Text) 
function rows($a)	{
 $b = mysql_num_rows($a) or die("Error: ");
 return $b;
}
function rows($a)	{
 $b = mysql_num_rows($a) or die("Error: ");
 return $b;
}