Query about SQL Injection in webpages
<p>Suppose you have a webpage requires you to input your username and password for authentication. </p>

<p>The username name "<strong><em>abs</em></strong>" and the password is "<strong><em>1234abcd</em></strong>" - you gain entry to the your profile. </p>

<p>But my question is, why is that if I input "<strong><em>abs' --</em></strong>" in the username field and no password, it still returns my profile page? </p>

<p>What is happening behind the scenes with the server, SQL and user?</p>

<p>I just cant seem to understand this. Thanks guys for any help. </p>