How do I get a boolean result from a SELECT query?

Question

I have the following SQLite QUERY in my PHP script:

try
  {
    //open the database
    $db = new PDO('sqlite:users.sqlite');

    //create the database or view existing
    $db->exec("CREATE TABLE USERS (Id INTEGER PRIMARY KEY, Type TEXT, Name TEXT,     Password TEXT)");    

    //select records with username and password match
    $existUser = $db->query("SELECT COUNT(*) FROM Users WHERE Name='" . $incomingusername . "' and Password ='" . $incomingpassword . "'");

    //check that either the result string isn't empty or somehow count rows   

    $result = sqlite_num_rows($existUser);
    print $result;
    echo "Done output from SQL<BR>";

    // close the database connection
    $db = NULL;
  }
catch(PDOException $e)
  {
    print 'Exception : '.$e->getMessage();
  }

I get an error from this: Fatal error: Call to undefined function sqlite_num_rows()

So I did some searching and it turns out that the language spec is a lie and this method doesn't exist. All I need is to test whether my sqlite database contains a username and password. I have also tried SELECT COUNT(*) FROM Users WHERE Name='Jeff' and Password ='Monhty'; but this doesn't return anything I am able to use, I don't understand the type of the return result. When I run this SELECT COUNT in a console against the database I get one result exactly, correct behaviour.

Please could someone indicate a SQL string that I can use that lets me treat its result as a Boolean in my PHP script? Many thanks.

Ninjaedit - ->numRows(); doesnt work either. Also not recognised.

Answer 1

You could change "SELECT COUNT(*) FROM..." to

"SELECT CAST((COUNT(*)=1) AS BOOLEAN) FROM..." 

if you want to check if exactly one user exists, or

"SELECT CAST((COUNT(*)>=1) AS BOOLEAN) FROM..." 

if you want to check if one or more users exist.

Answer 2

There are a few problems with your code:

First, you are trying to use sqlite_num_rows on a PDO handle. PDO is a database abstraction layer that works with many underlying database systems. sqlite_num_rows only works with handles from the native SQLite extension in PHP. So you can't use sqlite_num_rows here.

Secondly, SELECT COUNT(*) ... will always return 1 row, regardless of if there was a match found or not, for example:

SELECT COUNT(*) AS MyCount FROM Users WHERE Name = 'Jeff'

Will return a result set that looks something like this:

+---------+
| MyCount |
+---------+
| 1       |
+---------+

Assuming you have a row in the Users table that has the value Jeff in the Name column.

If, instead, you were to execute this:

SELECT COUNT(*) AS MyCount FROM Users WHERE Name = 'ThisDoesNotExist'

You would get a result set that looked like:

+---------+
| MyCount |
+---------+
| 0       |
+---------+

So you would still have 1 row, but the value of the MyCount column in the result set would tell you if a match was found or not. So even if you could use sqlite_num_rows here, it wouldn't help you because it would always return 1 .

What you really want to do is check the value of MyCount in the result set, and if it is 1 then there was a match, and if it is a 0 there was not a match.

Keep in mind that if there were multiple rows in your Users table that had the same Name and Password then COUNT(*) would return something the number of rows where that match occurred.

The following code should get you what you are looking for:

$existUser = false;

//select records with username and password match
$stmt = $db->prepare("SELECT COUNT(*) AS MyCount FROM Users WHERE Name = ? AND Password = ?");
if ($stmt->execute(array($incomingusername, $incomingpassword))) {
    $rows = $stmt->fetchAll();

    $existUser = ($rows[0]['MyCount'] == 1);
}

if ($existUser) {
    /* Found a matching user */
} else {
    /* Did NOT find a matching user */
}

The side effect of this approach is that you are protected from SQL injection .

Answer 3

Maybe..

$existUser = $db->query("SELECT COUNT(*) as count FROM Users WHERE Name='" . $incomingusername . "' and Password ='" . $incomingpassword . "'");
$row = $existUser->fetchAll();
$numRows = $row[0]['count'];