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 type of <input> creates a date input control, such as a pop-up calendar?
type="text" type="date" type="button"
<input type="date" name="set_date" value="2012-10-15" />
Which CSS property adds shadow effects to the text of an element?
font-style color text-shadow
h2 {
  text-shadow: 2px 3px 3px #a0a1fe;
}
Click on the function that adds new elements to the end of an array.
pop() shift() push()
var pags = ["lessons", "courses"];
pags.push("download", "tutorials");
alert(pags[2]);            // download
Which function sorts an array by key, in ascending order, maintaining key to data correlations?
asort() ksort() sort()
$lang = array(10=>"PHP", 20=>"JavaScript", "site"=>"coursesweb.net");
ksort($lang);
var_export($lang);     // array ("site"=>"coursesweb.net", 10=>"PHP", 20=>"JavaScript")
Insert, Select and Update NULL value in MySQL

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