Example implementation of inserting default values to SQLite fields given null values without changing your SQLite statement query.

sqlite_insert_default.php

<?php

// the name of your table
$table = "foobar";

// an array of your field names with default values
$fields = array(
	"foo" => 5,
	"bar" => "(date(now))"
);
$field_names = array_keys($fields);

// the data you want to insert
$data = array(
	"foo": 16
	// leave bar null to insert default value
);

// prepare the query
$insert_q = sprintf("INSERT INTO $table (%s) VALUES (%s)",
	implode(", ", $field_names),
	implode(", ", array_map("coalesce", $field_names))
	);
$stmt = $db->prepare($insert_q);

// bind values to the query
foreach($field_names as $field){
	$value = @$data[$field];
	$value_param = add_colon($field);

	if(empty($value)){
		$stmt->bindValue($value_param, null, PDO::PARAM_NULL);
	}else{
		$stmt->bindValue($value_param, $value);
	}
}

// execute the statement
$stmt->execute();

// coalesce mapping function
function coalesce($field){
	global $fields;
	$default = @$fields[$field];
	if(!empty($default)){
		return "coalesce(:$field, ".$default.")";
	}else{
		return ":$field";
	}
}

?>