In this tutorial you can learn how to work with NULL in MySQL tables: Insert, Update, and Select columns with NULL value.

Add column with NULL value

To insert into a MySQL table rows with columns having NULL, add the NULL value without quotes.
Example:
$sql = "INSERT INTO `table_name`
 (`column1`, `column2`, `column3`)
 VALUES
 ('val1', NULL, 'val3')";

Or, if the NULL value is stored into a variable, add "NULL" as a string to that variable, then write the variable into the SQL query, without quotes.
$nul = 'NULL';
$sql = "INSERT INTO `table_name`
 (`column1`, `column2`, `column3`)
 VALUES
 ('val1', $nul, 'val3')";

- If you create the $nul value like this:   $nul = NULL; , the SQL query will contain nothing in the place where this variable is added. Will result:
INSERT INTO `table_name` (`column1`, `column2`, `column3`) VALUES ('val1', , 'val3')

- If you want to insert the string "NULL", add it within quotes:
$sql = "INSERT INTO `table_name`
 (`column1`, `column2`, `column3`)
 VALUES
 ('val1', 'NULL', 'val3')";

UPDATE with NULL value

The same works with UPDATE.
Example:
$sql = "UPDATE `table_name` SET `column1`='val1', `column2`=NULL, WHERE `column3`='val3'";
Or:
$nul = 'NULL';
$sql = "UPDATE `table_name` SET `column1`='val1', `column2`=$nul, WHERE `column3`='val3'";

SELECT fields with NULL value

To select rows in a MySQL table according to columns with NULL value, use IS NULL.
Example:
$sql = "SELECT * FROM `table_name` WHERE `column` IS NULL";

If you want to Not return the rows with a specific NULL field, use IS NOT NULL.
$sql = "SELECT * FROM `table_name` WHERE `column` IS NOT NULL";

Daily Test with Code Example

HTML
CSS
JavaScript
PHP-MySQL
Which tag is used to add lists into <ul> and <ol> elements?
<dt> <dd> <li>
<ul>
 <li>http://coursesweb.net/html/</li>
 <li>http://coursesweb.net/css/</li>
</ul>
Which value of the "display" property creates a block box for the content and ads a bullet marker?
block list-item inline-block
.some_class {
  display: list-item;
}
Which instruction converts a JavaScript object into a JSON string.
JSON.parse() JSON.stringify eval()
var obj = {
 "courses": ["php", "javascript", "ajax"]
};
var jsonstr = JSON.stringify(obj);
alert(jsonstr);    // {"courses":["php","javascript","ajax"]}
Indicate the PHP class used to work with HTML and XML content in PHP.
stdClass PDO DOMDocument
$strhtml = '<body><div id="dv1">CoursesWeb.net</div></body>';
$dochtml = new DOMDocument();
$dochtml->loadHTML($strhtml);
$elm = $dochtml->getElementById("dv1");
echo $elm->nodeValue;    // CoursesWeb.net
Insert, Select and Update NULL value in MySQL

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