如何调试使用PHP和MySQL的基于数据库的表单?

I have 7 populated dropdown lists and I want it's values to be stored again into another table.

Now here is my code:

    <div id="main">
            <div id="sidebar">
                <h3>add documents</h3>
                <div class="bordered-form">

                <!-- PARA SA TEXTFIELDS -->
                <form class="add-docs" method="post">
                <ul class="linkedList">
                    <label>
                        Document Name:
                    </label>
                <div>
                    <input type="text" placeholder="Document Name" name="document_name"/>
                </div>

                    <label>
                        Amount:
                    </label>
                <div>
                    <input type="text" placeholder="Amount" name="document_amount"/>
                </div>


                <!-- Dropdowns Here -->
                <div>
                <label>
                    Requirement 1
                </label for="requirement">
                 <div class="form-group">

                 <div class="selectContainer">

                 <?php

                     $result=mysql_query($sql);
                     $options1="";
                     while ($row=mysql_fetch_array($result)) { 
                            $id=$row["requirement_id"]; 
                            $requirement_name=$row["requirement_name"]; 
                            $options1.="<OPTION VALUE=\"$requirement_name\">".$requirement_name;
                     }
                ?>
                <select name="requirement1" class="form-control SelectWidth">               
                <option  value="0">*Select a Requirement* <?=$options1?>
                </select>                   
                </div>
                </div>
                </div>


                <!-- Dropdowns Here -->
                <div>
                <label>
                    Requirement 2
                </label for="requirement">
                 <div class="form-group">

                 <div class="selectContainer">

                 <?php

                     $result=mysql_query($sql);
                     $options2="";
                     while ($row=mysql_fetch_array($result)) { 
                            $id=$row["requirement_id"]; 
                            $requirement_name=$row["requirement_name"]; 
                            $options2.="<OPTION VALUE=\"$requirement_name\">".$requirement_name;
                     }
                ?>
                <select name="requirement2" class="form-control SelectWidth">               
                <option  value="0">*Select a Requirement* <?=$options2?>
                </select>                   
                </div>
                </div>
                </div>

                    <!-- Dropdowns Here -->
                <div>
                <label>
                    Requirement 3
                </label for="requirement">
                 <div class="form-group">

                 <div class="selectContainer">

                 <?php

                     $result=mysql_query($sql);
                     $options3="";
                     while ($row=mysql_fetch_array($result)) { 
                            $id=$row["requirement_id"]; 
                            $requirement_name=$row["requirement_name"]; 
                            $options3.="<OPTION VALUE=\"$requirement_name\">".$requirement_name;
                     }
                ?>
                <select name="requirement3" class="form-control SelectWidth">               
                <option  value="0">*Select a Requirement* <?=$options3?>
                </select>                   
                </div>
                </div>
                </div>


                    <!-- Dropdowns Here -->
                <div>
                <label>
                    Requirement 4
                </label for="requirement">
                 <div class="form-group">

                 <div class="selectContainer">

                 <?php

                     $result=mysql_query($sql);
                     $options4="";
                     while ($row=mysql_fetch_array($result)) { 
                            $id=$row["requirement_id"]; 
                            $requirement_name=$row["requirement_name"]; 
                            $options4.="<OPTION VALUE=\"$requirement_name\">".$requirement_name;
                     }
                ?>
                <select name="requirement4" class="form-control SelectWidth">               
                <option  value="0">*Select a Requirement* <?=$options4?>
                </select>                   
                </div>
                </div>
                </div>

                    <!-- Dropdowns Here -->
                <div>
                <label>
                    Requirement 5
                </label for="requirement">
                 <div class="form-group">

                 <div class="selectContainer">

                 <?php

                     $result=mysql_query($sql);
                     $options5="";
                     while ($row=mysql_fetch_array($result)) { 
                            $id=$row["requirement_id"]; 
                            $requirement_name=$row["requirement_name"]; 
                            $options5.="<OPTION VALUE=\"$requirement_name\">".$requirement_name;
                     }
                ?>
                <select name="requirement5" class="form-control SelectWidth">               
                <option  value="0">*Select a Requirement* <?=$options5?>
                </select>                   
                </div>
                </div>
                </div>

                    <!-- Dropdowns Here -->
                <div>
                <label>
                    Requirement 6
                </label for="requirement">
                 <div class="form-group">

                 <div class="selectContainer">

                 <?php

                     $result=mysql_query($sql);
                     $options6="";
                     while ($row=mysql_fetch_array($result)) { 
                            $id=$row["requirement_id"]; 
                            $requirement_name=$row["requirement_name"]; 
                            $options6.="<OPTION VALUE=\"$requirement_name\">".$requirement_name;
                     }
                ?>
                <select name="requirement6" class="form-control SelectWidth">               
                <option  value="0">*Select a Requirement* <?=$options6?>
                </select>                   
                </div>
                </div>
                </div>

                    <!-- Dropdowns Here -->
                <div>
                <label>
                    Requirement 7
                </label for="requirement">
                 <div class="form-group">

                 <div class="selectContainer">

                 <?php

                     $result=mysql_query($sql);
                     $options7="";
                     while ($row=mysql_fetch_array($result)) { 
                            $id=$row["requirement_id"]; 
                            $requirement_name=$row["requirement_name"]; 
                            $options7.="<OPTION VALUE=\"$requirement_name\">".$requirement_name;
                     }
                ?>
                <select name="requirement7" class="form-control SelectWidth">               
                <option  value="0">*Select a Requirement* <?=$options7?>
                </select>                   
                </div>
                </div>
                </div>

                <br>
                <div>
                    <button name="btn-add" id="btnADD" type="submit" class="btn btn-info">ADD</button>
                    <button id="btnCANCEL" type="button" class="btn btn-info">CANCEL</button>

                </ul>
            </div>
            </div>




                </form>
        </div>
    </div>

I just want those 'requirement_name'/s from the 'requirements_tbl' to be stored into the other table named 'document_tbl'.

my php code the top of the html file is:

<?php

include_once 'dbconnect.php';
$sql="SELECT * FROM requirements_tbl";


if(isset($_POST['btn-add']))
{

$document_name = mysql_real_escape_string($_POST[ 'document_name' ]);
$document_amount = mysql_real_escape_string($_POST[ 'document_amount' ]);
$req1 = mysql_real_escape_string($_POST[ 'requirement1' ]);
$req2 = mysql_real_escape_string($_POST[ 'requirement2' ]);
$req3 = mysql_real_escape_string($_POST[ 'requirement3' ]);
$req4 = mysql_real_escape_string($_POST[ 'requirement4' ]);
$req5 = mysql_real_escape_string($_POST[ 'requirement5' ]);
$req6 = mysql_real_escape_string($_POST[ 'requirement6' ]);
$req7 = mysql_real_escape_string($_POST[ 'requirement7' ]);

$q="INSERT INTO document_tbl (document_name,document_amount,requirement1,requirement2,requirement3,requirement4,requirement5,requirement6,requirement7) VALUES('$document_name','$document_amount','$req1','$req2','$req3','$req4','$req5','$req6','$req7',)";




if( mysql_query($q)){


    ?>  
    <script>alert('Records successfully added!');</script>
    <?php
}


else{

    ?>
    <script>alert('Error while adding record!');</script>
    <?php
    }

}

?>

Your problem is here (code wrapped for readability):

$q="INSERT INTO document_tbl (
    document_name,document_amount,requirement1,requirement2,requirement3,requirement4,requirement5,requirement6,requirement7
) VALUES(
    '$document_name','$document_amount','$req1','$req2','$req3','$req4','$req5','$req6','$req7',
)";

If you examine the end of the VALUES clause, just inside the closing bracket, you can see a trailing comma, which SQL databases generally do not like. It will assume you wanted to provide another value, but then did not do so i.e. this is a syntax error.

As noted in the comments, this database engine is no longer supported, and you should move to PDO/MySQL or MySQLi as soon as you can.