PHP MySQL - UPDATE

Php-mysql Course

Once tables contain some data, you can edit and change those existing records with UPDATE statement.
The UPDATE command is used to change existing records in a table.

  - Syntax:

UPDATE table_name
 SET column1=value, column2=value2,...
 WHERE some_column=some_value

- The WHERE clause is important in a UPDATE query, it tells MySQL which record or records should be updated. If you omit the WHERE clause, all rows will be affected!
- The UPDATE statement is sent to the MySQL server with the query() method of the mysqli object.

  - Example
In the previous lessons was created a table named "users" and we added some data in it. Here is how it looks the first two records.

id	name	password	email	reg_date
1	Marius	faith	name@domain.net	2011-03-24 09:51:46
2	MarPlo	peace	user@domain.com	2011-03-24 10:10:27

In this example, we'll change the email for the user with the "name" MarPlo.

<?php
// connect to the "tests" database
$conn = new mysqli('localhost', 'root', 'pass', 'tests');

// check connection
if (mysqli_connect_errno()) {
  exit('Connect failed: '. mysqli_connect_error());
}

// UPDATE sql query
$sql = "UPDATE `users` SET `email`='new_mail@domain.net' WHERE `name`='MarPlo' AND `id`=2";

// perform the query and check for errors
if (!$conn->query($sql)) {
  echo 'Error: '. $conn->error;
}

$conn->close();
?>

As you can see, the WHERE clause sets two conditions with the "AND" operator (WHERE `name`='MarPlo' AND `id`=2), this tells MySQL to update only the rows that have "name='MarPlo'" and "id=2". Setting these two conditions, we are shure that only that row will be updated, not other row with the same name.
Also, you can apply the LIMIT option to set how many rows to be updated.
Example:
                $sql = "UPDATE `users` SET `email`='new_mail@domain.net' WHERE `name`='MarPlo' AND `id`=2 LIMIT 1";

After the update, the first two rows in "users" table will look like this: - Becouse "reg_date" is a TIMESTAMP column (with attribute:   on update CURRENT_TIMESTAMP ), MySQL server has updated its value too, changing it with the current date and time when the update was performed.
If you want an update to not affect the value of a TIMESTAMP column, when you create the table you must not add the "on update" attribute, only the DEFAULT ( `column_date` TIMESTAMP NOT NULL DEFAULT CURRENT_TIMESTAMP ).

- If you perform an update query that doesn't actually change any values (becouse the WHERE condition doesn't match any row), you won't see any errors but no rows will be affected.
- It's indicated to not change the value of a primary-key column (in the example above, the "id" column).

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