Display message on same page

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Dear All

 

I want to display message on same customised popup window . Say for eg when i click on signin link a popup window comes and when i click on submit button , it get redirected to loginpage.php where php code for connection is written and other code of php is wriiten for database fetching . and if login credential match it get redirected to main page

 

So what i want to do is when some one click on signin link and popup window open up and when clicked on submit button , if the credential dont match it should throw error on same popup window before it closes