如何将实际的 NULL 值插入到可为空的列中？

Question

function save($gmt, $name, $address, $phone, $remark)
{
    $query= "INSERT INTO `user` (`gmt`, `name`, `address`, `phone`, `remark`) VALUES ('$gmt', '$name', '$address', '$phone', '$remark')";
    mysql_query($query);
}

Here, address, phone, and remark can be NULL . I need it to save NULL whenever the variable is set to NULL and the column is nullable, instead of inserting an empty string.

How can I insert NULL value into the database using PHP?

Answer 1

This is PHP solution, but you have to use mysqli because mysql deprecated, please read more about mysqli . Also, you must consider SQL injection

function save($gmt, $name, $address, $phone, $remark)
{
  if(empty($phone)){
   $phone = 'NULL';
  }else{
   $phone = "'".$phone."'";
  }
  if(empty($remark)){
   $remark = 'NULL';
  }else{
   $remark = "'".$remark."'";
  }
    $query= "INSERT INTO `user` (`gmt`, `name`, `address`, `phone`, `remark`) VALUES ('$gmt', '$name', '$address', $phone, $remark)";
    mysql_query($query);
}
//tests
save("a", "b", "c", "", "")."<br>";
save("a", "b", "c", "d", "")."<br>";
save("a", "b", "c", "d", "e")."<br>";
/*
INSERT INTO `user` (`gmt`, `name`, `address`, `phone`, `remark`) VALUES ('a', 'b', 'c', NULL, NULL)
INSERT INTO `user` (`gmt`, `name`, `address`, `phone`, `remark`) VALUES ('a', 'b', 'c', 'd', NULL)
INSERT INTO `user` (`gmt`, `name`, `address`, `phone`, `remark`) VALUES ('a', 'b', 'c', 'd', 'e')
*/
?>

DEMO

Answer 2

Try switching to prepared statements (which as a bonus is less prone to SQL injections).

function save($gmt, $name, $address, $phone, $remark)
{
    if(!isset($phone) || empty($phone)) { $phone = null; }
    if(!isset($remark) || empty($remark) { $remark = null; }

    $db = new PDO(...);

    $stmt = $db->prepare("INSERT INTO `user` (`gmt`, `name`, `address`, `phone`, `remark`) VALUES (:gmt, :name, :address, :phone, :remark)");
    $stmt->bindValue("gmt", $gmt, PDO::PARAM_STR);
    $stmt->bindValue("name", $name, PDO::PARAM_STR);
    $stmt->bindValue("address", $address, PDO::PARAM_STR);
    $stmt->bindValue("phone", $phone, PDO::PARAM_STR);
    $stmt->bindValue("remark", $remark, PDO::PARAM_STR);
    $stmt->execute();
}

This will handle the null values correctly in MySQL

Answer 3

PHP doesn't print NULL - it is just an empty string. So in your example you will try to insert '' , which in SQL again is an empty string.

You have to use NULL (without quotes).

And the best practice to achieve that is to use an ORM or a PHP framework with a database abstraction layer which does this for you.

Answer 4

Using ternary operator, you can also use this

$add = ($address == '' ? NULL : $address);
$phn = ($phone == '' ? NULL : $phone);
$rmk = ($remark == '' ? NULL : $remark);

Answer 5

fields can be NULL

-> qtd_aulas_previstas

-> qtd_aulas_dadas

$qtd_aulas_previstas = ( empty($qtd_aulas_previstas) ? 'NULL' : "'".$qtd_aulas_previstas."'");
$qtd_aulas_dadas     = ( empty($qtd_aulas_dadas)     ? 'NULL' : "'".$qtd_aulas_dadas."'");


//insere os dados na tabela
$inserir_tb = mysqli_query($conexao, "INSERT INTO tb_turma_bimestre VALUES('', '$cod_turma', '$cod_bimestre', $qtd_aulas_previstas, $qtd_aulas_dadas, '$data_abertura', '$data_encerramento', '$date_time', '$nome_login')")or die("Error2: " .mysqli_error($conexao));