Asked  7 Months ago    Answers:  5   Viewed   44 times

I'm struggling with some PHP/MySQL code. I am reading from 1 table, changing some fields then writing to another table, nothing happens if inserting and one of the array values is null when I would like it to insert null in the database (null values are allowed for the field). It looks a bit like this:

$results = mysql_query("select * from mytable");
while ($row = mysql_fetch_assoc($results) {
    mysql_query("insert into table2 (f1, f2) values ('{$row['string_field']}', {$row['null_field']});

Not every row has a null value and in my query there are more fields and 2 columns which may or may not be null



This is one example where using prepared statements really saves you some trouble.

In MySQL, in order to insert a null value, you must specify it at INSERT time or leave the field out which requires additional branching:

INSERT INTO table2 (f1, f2)
  VALUES ('String Value', NULL);

However, if you want to insert a value in that field, you must now branch your code to add the single quotes:

INSERT INTO table2 (f1, f2)
  VALUES ('String Value', 'String Value');

Prepared statements automatically do that for you. They know the difference between string(0) "" and null and write your query appropriately:

$stmt = $mysqli->prepare("INSERT INTO table2 (f1, f2) VALUES (?, ?)");
$stmt->bind_param('ss', $field1, $field2);

$field1 = "String Value";
$field2 = null;


It escapes your fields for you, makes sure that you don't forget to bind a parameter. There is no reason to stay with the mysql extension. Use mysqli and it's prepared statements instead. You'll save yourself a world of pain.

Wednesday, March 31, 2021
answered 7 Months ago

The mysqli_num_rows() function returns the number of rows in a result set. For insert, update and delete use mysqli_affected_rows

Wednesday, March 31, 2021
answered 7 Months ago

Yes, bindParam binds a parameter to a variable name (reference), not a value, as the manual says.

However, there's a simpler syntax for your situation. PDOStatement::execute can take an array of values.

public function insert($table, $cols, $values){

    $placeholder = array();
    for ($i = 0; i < count($values); $i++)
      $placeholder[] = '?';

    $sql = 'INSERT INTO '. $table . ' (`' . implode("`, `", $cols) . '`) ';
    $sql.= 'VALUES (' . implode(", ", $placeholder) . ')';

    $stmt = $this->dbh->prepare($sql);

Wednesday, March 31, 2021
answered 7 Months ago

My tables were InnoDB tables and when i changed my tables to MyISAM the insert worked fine. Well i have never encountered this problem before. Well that did the trick for the time being.

If i want to use InnoDB engine for transactions? How can i get php to be able to insert values in InnoDB table? Any one got any suggestion? And i am using WAMP server and the MySQL is version 5.5.24. And i did change the InnoDB conf in my.ini but that did not seem to work either?

Wednesday, March 31, 2021
answered 7 Months ago

I would rather suggest to check $_POST paramenters before definied them so if a variable is not empty set values otherwise set as NULL

if(!empty($_POST['dateRequest'])) { $dateRequest = $_POST['dateRequest']; } else { $dateRequest = NULL; }
if(!empty($_POST['firstName'])) { $firstName = $_POST['firstName']; } else { $firstName  = NULL; }
if(!empty($_POST['lastName'])) { $lastName = $_POST['lastName']; } else { $lastName = NULL; }
if(!empty($_POST['lastName'])) { $note = $_POST['note']; } else { $note = NULL; }

This will prevent you to pass empty parameters in your query.

Saturday, May 29, 2021
answered 5 Months ago
Only authorized users can answer the question. Please sign in first, or register a free account.
Not the answer you're looking for? Browse other questions tagged :