empty field to mysql using php

try this

if ( !empty($_POST['expert_name']) ){
   $sql="INSERT INTO experts(id,expert_name) VALUES(NULL, '$expert_name')";
   $result=mysql_query($sql);
}

if ( !empty($_POST['expert_name2']) ){
   $sql2="INSERT INTO experts(id,expert_name) VALUES(NULL, '$expert_name2')";
   $result2=mysql_query($sql2);
}

if ( !empty($_POST['expert_name3']) ){
   $sql3 ="INSERT INTO experts(id,expert_name) VALUES(NULL, '$expert_name3')";
   $result3 =mysql_query($sql3 );
}

Then you might want to check if the variable is empty().

<?php

include("connect.php");


$expert_name  = trim($_POST['expert_name']);
$expert_name2 = trim($_POST['expert_name2']);
$expert_name3 = trim($_POST['expert_name3']);


// this is for arabic language.
mysql_query("SET NAMES utf8");

// Insert data into mysql 
if(!empty($expert_name)) {
$sql="INSERT INTO experts(id,expert_name) VALUES(NULL, '$expert_name')";
$result=mysql_query($sql);
}     
if(!empty($expert_name2)) {
$sql2="INSERT INTO experts(id,expert_name) VALUES(NULL, '$expert_name2')";
$result2=mysql_query($sql2);
}
if(!empty($expert_name3)) {
$sql3="INSERT INTO experts(id,expert_name) VALUES(NULL, '$expert_name3')";
$result3=mysql_query($sql3);
}
// if successfully insert data into database, displays message "Successful". 
if($result){
echo "Successful";
echo "<BR>";
// echo "<a href='formadd.php'>Back to main page</a>";
}
else {
echo "ERROR";
echo "<br>";
// this for print error in insert process 
echo mysql_error();
echo "<a href='expert_add.php'><br>Please try again </a>";
}

Also note: You only check if $result is okay. If you only fill textbox 2 and leave 1 empty, the value of 2 it will get inserted but an error is shown.

I'd say your code need general review, but as it is for now you will have to do something like this each query:

if (!empty($expert_name2){
    $result2=mysql_query($sql2)
}

But you should try to loop your queries in foreach rather than manually write every on query. And by the way:

if($result){
echo "Successful";
echo "<BR>";
// echo "<a href='formadd.php'>Back to main page</a>";
}

This code only return succes when 1st wuery success because you use $result which is set in 1st query only

The ID is probably NOT NULL AUTO_INCREMENT, so that won't accept NULL as value. try sending blank value, such as:

$sql="INSERT INTO experts(id,expert_name) VALUES ('', '$expert_name')";

Also, build bulk insert, rather than multiple. I will explain why, when you insert single insert into the database, the values being inserted, then, the DB engine flushes indexes (they written to disk), unless you have set delay_key_write=ALL in you my.cnf. Index flushing directly affects your db performance.

Please, check the reworked code out. The code adjusted for bulk insert, sql string escaping for security purposes and additional verification for post keys existence.

<?php
include("connect.php");

// this is for arabic language.
mysql_query("SET NAMES utf8");
$values = array();
$skipInsert = true;
$fields = array('expert_name', 'expert_name2', 'expert_name3');
$insert = "INSERT INTO experts(id,expert_name) VALUES ";
// Loop through predefined fields, and prepare values.
foreach($fields AS $field) {
    if(isset($_POST[$field]) && !empty($_POST[$field])) {
        $values[] = "('', '".mysql_real_escape_string(trim($_POST[$field]))."')";
    }
}

if(0 < sizeof($values)) {
    $skipInsert = false;
    $values = implode(',', $values);
    $insert .= $values;
}

if(false === $skipInsert) {
    mysql_query($insert);
}
// if successfully insert data into database, displays message "Successful".
if($result){
    echo "Successful","<BR>";
    // echo "<a href='formadd.php'>Back to main page</a>";
} else {
    echo "ERROR","<br>",mysql_error(),"<a href='expert_add.php'><br>Please try again </a>";
}

HTH, VR

if(!empty($textbox1_value)) {

   //DO SQL

}

You can repeat this for multiple boxes however you wish, the empty operator checks if its empty, so if its not empty the "//DO SQL" area will get run.