writing fetch_assoc() array data to table - php

Question

What is the proper way to reference the array components from fetch_assoc() so that they can be inserted into another table?
Here is my current code:
$sql_read = "SELECT id, data1, data2, date FROM `table1`";
$result = $mysqli->query($sql_read);
if ($result !== false) {
$rows = $result->fetch_all();
}
while ($row = $result->fetch_assoc()){
$sql_write = "INSERT INTO `table2`.`load_records` (`id`, `data1`,`data2`,`date`) VALUES ('.$row['id']', '.$row['data1']', '.$row['data2']', '.$row['date']', NULL);";
}

Answer 1

As suggested in my comment, first your select statement should be:
"SELECT id, data1, data2, date FROM `table1`";
Furthermore, the insert statement should be (see the use of concatenation of strings):
"INSERT INTO `table2`.`load_records` (`id`, `data1`,`data2`,`date`) VALUES ('".$row['id']."', '".$row['data1']."', '".$row['data2']."', '".$row['date']."', NULL);";

Answer 2

There are some errors in your script, as already pointed out.
But you might also be interested in the INSERT INTO ... SELECT variant of the INSERT syntax.
<?php
$query = '
INSERT INTO
table2
(`id`, `data1`,`data2`,`date`)
SELECT
`id`, `data1`,`data2`,`date`
FROM
table1
';
$result = $mysqli->query($query);
if ( !$result ) {
trigger_error('error: ' . $mysqli->error, E_USER_ERROR);
}
else {
echo $mysqli->affected_rows, ' rows have been transfered';
}

Answer 3

You have an extra field in the VALUES that is not referenced in the INTO and the concatenation of the row data is incorrect;
$sql_write = "INSERT INTO `table2`.`load_records`
(`id`, `data1`,`data2`,`date`)
VALUES ('.$row['id'].', '.$row['data1']', '.$row['data2']', '.$row['date']', NULL);";
should be:
$sql_write = "INSERT INTO `table2`.`load_records`
(`id`, `data1`,`data2`,`date`)
VALUES ('".$row['id']."', '".$row['data1']."', '".$row['data2']."', '".$row['date']."');";
Or you need to update the INTO to include an extra column that accepts NULL
See also:
The PHP reference on mysqli_result::fetch_assoc