ีupdate 2 table ขึ้น ambiguous รบกวนช่วยหน่อยค่ะมีอะไรตกหล่นค่ะ

                        <!--Edit Item Modal -->
                        <div id="edit<?php echo $section_id; ?>" class="modal fade" role="dialog">
                        <form method="post" class="form-horizontal" role="form">
                            <div class="modal-dialog modal-lg">
                                <!-- Modal content-->
                                <div class="modal-content">
                                    <div class="modal-header">
                                        <button type="button" class="close" data-dismiss="modal">&times;</button>
                                        <h4 class="modal-title">แก้ไขข้อมูล</h4>
                                    </div>
                                    <div class="modal-body">
                                        <input type="hidden" name="edit_item_id" value="<?php echo $section_id; ?>">
                                        <input type="hidden" name="edit_dep_id" value="<?php echo $department_id; ?>">
                                        <div class="form-group">
                                          <label class="control-label col-sm-2" for="department_name">ชื่อหน่วยงาน:</label>
                                          <div class="col-sm-4">
                                             <input type="text"  class="form-control" id="department_name" name="department_name"
                                             value="<?php echo $department_name; ?>"  placeholder="department_name" required> </div>
                                             <br><br>

                                            <label class="control-label col-sm-2" for="section_name">xxxx</label>
                                            <div class="col-sm-4">
                                            <input type="text" class="form-control" id="section_name" name="section_name"
                                            value="<?php echo $section_name; ?>" placeholder="section_name" required> </div>
                                              <br><br>

                                            <label class="control-label col-sm-2" for="phone">xxxx</label>
                                            <div class="col-sm-4">
                                              <input type="text" class="form-control" id="phone" name="phone"
                                              value="<?php echo $phone; ?>" placeholder="phone" required></div><br><br>

                                            <label class="control-label col-sm-2" for="building_name">xxxx</label>
                                            <div class="col-sm-4">
                                             <input type="text" readonly class="form-control" id="building_name" name=
                                             "building_name"
                                                value="<?php echo $building_name; ?>" placeholder="building_name" required> </div>
                                                <br><br>
                                            <label class="control-label col-sm-2" for="floor">xxxx:</label>
                                            <div class="col-sm-4">
                                               <input type="text" readonly class="form-control" id="floor" name="floor"
                                               value="<?php echo $floor; ?>"  placeholder="floor" required> </div>
                                               <br><br>
                                        </div>
                                    </div>
                                    <div class="modal-footer">
                                        <button type="submit" class="btn btn-primary" name="update_item"><span class="glyphicon
                                        glyphicon-edit"></span> Edit</button>
                                        <button type="button" class="btn btn-warning" data-dismiss="modal"><span class="glyphicon
                                        glyphicon-remove-circle"></span> Cancel</button>
                                    </div>
                                </div>
                            </div>
                        </form>
                    </div>
 

                       //Update Items
                        if(isset($_POST['update_item'])){
                            $edit_item_id = $_POST['edit_item_id'];
                            $edit_dep_id = $_POST['edit_dep_id'];
                            $department_name = $_POST['department_name'];
                            $section_name = $_POST['section_name'];
                            $phone = $_POST['phone'];
                            $building_name = $_POST['building_name'];
                            $floor = $_POST['floor'];

                            $sql = "UPDATE section SET section_name='$section_name',phone='$phone'
                                    WHERE section_id ='$edit_item_id' ";

                            $sql = "UPDATE department,section  SET department_name='$department_name'
                                    WHERE department_id ='$edit_dep_id' and section_id ='$edit_item_id' ";

                                    if ($conn->query($sql) === TRUE) {
                                        echo '<script>window.location.href="inventory2.php"</script>';

                                    } else {
                                        echo "Error deleting record: " . $conn->error;
                                    }
                                }


///////////////////////////////
 มันขึ้น แบบนี้อะค่ะ Error deleting record: Column 'department_id' in where clause is ambiguous
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