Specifies a default value for a column. With one exception, the default value must be a constant; it cannot be a function or an expression. This means, for example, that you cannot set the default for a date column to be the value of a function such as NOW() or CURRENT_DATE. The exception is that you can specify CURRENT_TIMESTAMP as the default for a TIMESTAMP or DATETIME column.https://dev.mysql.com/doc/refman/5.7/en/create-tab...
Почему не сделать jsone_decode? Потому что мне приходит как json, так и обычные формы через $_POST, $_GETи какое это имеет отношение к вопросу?
$data = [
'1,2,3',
'4,5,6',
'7,8,9'
];
header('Content-Type: text/csv');
header('Content-disposition: attachment;filename=data.csv');
foreach ($data as $row) {
echo $row, PHP_EOL;
}