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 attribute is used in <img> tag for the address of the image?
href src rel
<img src="http://coursesweb.net/imgs/webcourses.gif" width="191" height="63" alt="Courses-Web" />
Which CSS code hides the element on page?
display: none; display: inline; position: relative;
#id {
  display: none;
}
What instruction stops the execution of a while() or for() statement?
continue prompt() break
for(var i = 0; i< 8; i++) {
  if(i > 1) break;
  alert(i);
}
Indicate the function that can create a constant.
define() include() defined()
define("CONSTANT_NAME", "value");
echo CONSTANT_NAME;
Insert, Select and Update NULL value in MySQL

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