<?php echo $_SERVER['PHP_SELF'];?>

<form action='<?php echo $_SERVER['PHP_Self']; ?>'>
<input type='text' name='field1' value='<?php if(isset($field1)){echo $field1; } ?>'>
<input type='text' name='field2' value='<?php if(isset($field2)){echo $field2; } ?>'>
<input type='text' name='field3' value='<?php if(isset($field3)){echo $field3; } ?>'>
<input type='text' name='field4' value='<?php if(isset($field4)){echo $field4; } ?>'>
<input type='submit' onclick="return confirm('Are all fields complete?')">

<?php 
/* 
logical construct depends on your data,,,
validate data entries, 
if valid 
 insert to mysql, 
 disable submit so data will not be aded to table twice, 
 or redirect to another page 
else
 echo feedback to user to explain what is right/wrong with the submitted data  before the form is resubmitted
*/  ?>
<form action='<?php iecho $_SERVER['PHP_Self']; ?>'>
<input type='text' name='field1' value='<?php if(isset($field1)){echo $field1; } ?>'>
<input type='text' name='field2' value='<?php if(isset($field2)){echo $field2; } ?>'>
<input type='text' name='field3' value='<?php if(isset($field3)){echo $field3; } ?>'>
<input type='text' name='field4' value='<?php if(isset($field4)){echo $field4; } ?>'>
<input type='submit' onclick="return confirm('Are all fields complete?')">