Assign One Time Username in PHPMYSQL - php

Question

i am working on a login Script. I have a registration and its login, what i need to give a single access/login, i have my fields in database table name is qz_userauth as ID fname lname email username password. Restrict login after one attempt. Possible ?
Here is login Form
<form action="functions.php" method="post" id="login">
<fieldset>
<legend>Login </legend>
<ul>
<li>
<label for="username"><span class="required">Username</span></label>
<input id="username" name="username" class="text required" type="text" />
<label for="username" class="error">This field cannot be empty</label>
</li>
<li>
<label for="password"><span class="required">Password</span></label>
<input name="password" type="password" class="text required" id="password" maxlength="20" />
</li>
<?php if($_SESSION['LCNT']>=4){ ?>
<li>
<p id="p-captcha">
<div id="captchaImg"><img id="captcha" src="captcha/securimage_show.php" alt="CAPTCHA Image" /></div>
<div id="captchaInput"><input type="text" name="captcha_code" size="16" maxlength="6" value="Enter Captcha" /></div>
<div id="captchaRefresh"><img src="captcha/images/refresh.gif" /></div>
</p>
</li>
<?php } ?>
<li>
<label class="centered info"><a id="forgotpassword" href="fpass.php">Forgot Your password...</a></label>
</li>
</ul>
</fieldset>
<input type="hidden" name="action" value="login" />
<fieldset class="submit">
<input type="submit" class="sbutton" value="Login" /> <input type="button" class="sbutton" value="Register" onclick="window.location='register.php'" />
</fieldset>
</form>

Answer 1

Just set one more field in the table as flag. and after one login attempt set the value of flag as false. and check the flag value during login.

Answer 2

If you mean to ask you want to allow only 1 login at a time per user then you can add another field to your table something like login_status. Set this to 1 when user is logged in and 0 on logout. Then in your login script check if this is 0, only then allow login