Check If a Row Exists Using Old MySQL_* API

Check if a row exists using old mysql_* API

This ought to do the trick: just limit the result to 1 row; if a row comes back the $lectureName is Assigned, otherwise it's Available.

function checkLectureStatus($lectureName)
{
    $con = connectvar();
    mysql_select_db("mydatabase", $con);
    $result = mysql_query(
        "SELECT * FROM preditors_assigned WHERE lecture_name='$lectureName' LIMIT 1");

    if(mysql_fetch_array($result) !== false)
        return 'Assigned';
    return 'Available';
}

Best way to test if a row exists in a MySQL table

You could also try EXISTS:

SELECT EXISTS(SELECT * FROM table1 WHERE ...)

and per the documentation, you can SELECT anything.

Traditionally, an EXISTS subquery starts with SELECT *, but it could
begin with SELECT 5 or SELECT column1 or anything at all. MySQL
ignores the SELECT list in such a subquery, so it makes no difference.

How to check if a row exists in MySQL? (i.e. check if username or email exists in MySQL)

The following are tried, tested and proven methods to check if a row exists.

(Some of which I use myself, or have used in the past).

Edit: I made an previous error in my syntax where I used mysqli_query() twice. Please consult the revision(s).

I.e.:

if (!mysqli_query($con,$query)) which should have simply read as if (!$query).

I apologize for overlooking that mistake.

Side note: Both '".$var."' and '$var' do the same thing. You can use either one, both are valid syntax.

Here are the two edited queries:

$query = mysqli_query($con, "SELECT * FROM emails WHERE email='".$email."'");

    if (!$query)
    {
        die('Error: ' . mysqli_error($con));
    }

if(mysqli_num_rows($query) > 0){

    echo "email already exists";

}else{

    // do something

}

and in your case:

$query = mysqli_query($dbl, "SELECT * FROM `tblUser` WHERE email='".$email."'");

    if (!$query)
    {
        die('Error: ' . mysqli_error($dbl));
    }

if(mysqli_num_rows($query) > 0){

    echo "email already exists";

}else{

    // do something

}

You can also use mysqli_ with a prepared statement method:

$query = "SELECT `email` FROM `tblUser` WHERE email=?";

if ($stmt = $dbl->prepare($query)){

        $stmt->bind_param("s", $email);

        if($stmt->execute()){
            $stmt->store_result();

            $email_check= "";         
            $stmt->bind_result($email_check);
            $stmt->fetch();

            if ($stmt->num_rows == 1){

            echo "That Email already exists.";
            exit;

            }
        }
    }

Or a PDO method with a prepared statement:

<?php
$email = $_POST['email'];

$mysql_hostname = 'xxx';
$mysql_username = 'xxx';
$mysql_password = 'xxx';
$mysql_dbname = 'xxx';

try {
$conn= new PDO("mysql:host=$mysql_hostname;dbname=$mysql_dbname", $mysql_username, $mysql_password); 
     $conn->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
} catch (PDOException $e) {
     exit( $e->getMessage() );
}

// assuming a named submit button
if(isset($_POST['submit']))
    {

        try {
            $stmt = $conn->prepare('SELECT `email` FROM `tblUser` WHERE email = ?');
            $stmt->bindParam(1, $_POST['email']); 
            $stmt->execute();
            while($row = $stmt->fetch(PDO::FETCH_ASSOC)) {

            }
        }
        catch(PDOException $e) {
            echo 'ERROR: ' . $e->getMessage();
        }

    if($stmt->rowCount() > 0){
        echo "The record exists!";
    } else {
        echo "The record is non-existant.";
    }

    }
?>

Prepared statements are best to be used to help protect against an SQL injection.

N.B.:

When dealing with forms and POST arrays as used/outlined above, make sure that the POST arrays contain values, that a POST method is used for the form and matching named attributes for the inputs.

FYI: Forms default to a GET method if not explicity instructed.

Note: <input type = "text" name = "var"> - $_POST['var'] match. $_POST['Var'] no match.

POST arrays are case-sensitive.

Consult:

http://php.net/manual/en/tutorial.forms.php

Error checking references:

http://php.net/manual/en/function.error-reporting.php
http://php.net/manual/en/mysqli.error.php
http://php.net/manual/en/pdo.error-handling.php

Please note that MySQL APIs do not intermix, in case you may be visiting this Q&A and you're using mysql_ to connect with (and querying with).

You must use the same one from connecting to querying.

Consult the following about this:

Can I mix MySQL APIs in PHP?

If you are using the mysql_ API and have no choice to work with it, then consult the following Q&A on Stack:

MySql php: check if Row exists

The mysql_* functions are deprecated and will be removed from future PHP releases.

It's time to step into the 21st century.

You can also add a UNIQUE constraint to (a) row(s).

References:

http://dev.mysql.com/doc/refman/5.7/en/constraint-primary-key.html
http://dev.mysql.com/doc/refman/5.7/en/alter-table.html
How to check if a value already exists to avoid duplicates?
How add unique key to existing table (with non uniques rows)

How to compare MySql data exist in php

Try this way:-

    $servername = "localhost";
    $username = "your_username";
    $password = "your_password";
    $dbname = "your_db";

    // Create connection
    $conn = new mysqli($servername, $username, $password, $dbname);
    // Check connection
    if ($conn->connect_error) {
        die("Connection failed: " . $conn->connect_error);
    } 

    if (isset($_POST['btnReg'])) {

      $user2=mysqli_real_escape_string($conn, $_POST["reg_user"]);
     // mysqli_real_escape_string is used instead of mysql_real_escape_string

         $sql =  "SELECT * FROM accounts WHERE Username = '$user2' LIMIT 1";
         $result = $conn->query($sql);

        if ($result->num_rows > 0) {
           echo '<div class="alert alert-danger"><strong>Username already exists</strong></div>';
           } 
           else {
           echo '<div class="alert alert-success"><strong>Sign Up Success .</strong></div>';
           }
    }
    $conn->close();

Check if MySQL table exists or not

Updated mysqli version:

if ($result = $mysqli->query("SHOW TABLES LIKE '".$table."'")) {
    if($result->num_rows == 1) {
        echo "Table exists";
    }
}
else {
    echo "Table does not exist";
}

Original mysql version:

if(mysql_num_rows(mysql_query("SHOW TABLES LIKE '".$table."'"))==1) 
    echo "Table exists";
else echo "Table does not exist";

Referenced from the PHP docs.

Differentiate between 'no rows were affected' and rows succesfully UPDATEd--to same value (MySQL and PHP)

A simple solution would be two queries.

First, run a SELECT query to check if the row exists using mysqli_num_rows().

Then, if the row exists, you can run the UPDATE query and use mysqli_affected_rows().

[EDIT]

...I'll suggest a potential alternative for anyone seeking out a single call. I don't know if you are interested in doing any INSERTs, or purely UPDATEs. Below is some food for thought:

From the top comment @ http://php.net/manual/en/mysqli.affected-rows.php :

On "INSERT INTO ON DUPLICATE KEY UPDATE" queries, though one may expect affected_rows to return only 0 or 1 per row on successful queries, it may in fact return 2.

From Mysql manual: "With ON DUPLICATE KEY UPDATE, the affected-rows value per row is 1 if the row is inserted as a new row and 2 if an existing row is updated."

See: http://dev.mysql.com/doc/refman/5.0/en/insert-on-duplicate.html

Here's the sum breakdown per row:

+0: a row wasn't updated or inserted (likely because the row already existed, but no field values were actually changed during the UPDATE)

+1: a row was inserted

+2: a row was updated

Can you make that suit your needs?

Check If a Row Exists Using Old MySQL_* API