Using mysql_num_rows(), how do I tell whether myql_query() has returned a result of 0 or an sql error in php

Question

Using php I understand that false is the same as 0, so when checking my select query results, if I have 0 results mysql_num_rows($result) will evaluate to false - this i understand, what will the function evaluate to if I have an sql error.

$sqlQuery="SELECT userID, userName, password, role From User WHERE userName=$userName;"
$result=mysql_query($sqlQuery);
if(mysql_num_rows($result)){
    #I have results so process
} else #do I have an error or do I just have no results

I need to return a meaningful result from the query i.e. "no such user" or details of the sql error, I do not wish to use mysql_query($sqlQuery) or die(). I have searched the web and can't find a conclusive answer. Any help would be greatly appreciated.

Amanda

Did you surround with quotes `$userName` ? – Fabio Mora Jul 19 '11 at 12:50 — Fabio Mora, Jul 19 '11 at 12:50

Andreas Wong · Answer 1 · 2011-07-19T12:56:31.677

You can check using ===

if(($result = mysql_query('select * from foo')) === false) {
   // mysql error
} else {
   if(mysql_num_rows($result) == 0) echo 'no such user.';
}

or if you just want to modify your code, you could go with:

$sqlQuery="SELECT userID, userName, password, role From User WHERE userName=$userName;"
$result=mysql_query($sqlQuery);
if(mysql_num_rows($result)){
    #I have results so process
} else {
    #do I have an error 
    if($result === false) {
        // mysql error indeed

    #or do I just have no results
    } else { 
        echo 'no such user';
    }
}

score 1 · Answer 2 · answered Jul 19 '11 at 12:49

1

$res=mysql_query('smth');
if(mysql_error()){//error
}
else{//correct, you can check mysql_num_rows
}

answered Jul 19 '11 at 12:49

RiaD

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Pretty sure `smth` isn't valid SQL :) – Michael Berkowski Jul 19 '11 at 12:52
@Michael. I think OP can understand it and replace with your iwn query:) – RiaD Jul 19 '11 at 12:53

score 1 · Answer 3 · answered Jul 19 '11 at 12:54

mysql_query() will return false on error, and the result resource otherwise. mysql_num_rows() will throw a warning if you send it false, so you need to determine if the query worked anyway

$result = mysql_query($query);
if ($result === false) {
   //handle error
}
else if (mysql_num_rows($result)) {
   //handle rows
}
else {
   //handle no rows
}

Warface · Answer 4 · 2011-07-19T12:56:21.217

0

if(mysql_num_rows($result) != 0){
    #I have results so process
} else{ 
    echo 'No such user';
}

edited Jul 19 '11 at 12:56

answered Jul 19 '11 at 12:49

Warface

5,029
9
56
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I think you misunderstood the question – Explosion Pills Jul 19 '11 at 12:53

score 0 · Answer 5 · answered Jul 19 '11 at 12:59

You can use PHP's typed comparison operators to differentiate between 0 and false. So your test would become:

$num_rows = mysql_num_rows($result);
if($num_rows > 0){
    #I have results so process
} else if ($num_rows === false) {
    #An error occured: use mysql_error for details
} else {
    #No errors, no results either
}

Using mysql_num_rows(), how do I tell whether myql_query() has returned a result of 0 or an sql error in php

5 Answers5