/**
* Compile the SQL query and return it.
*
* @param object Database instance
* @return string
*/
public function compile(Database $db)
{
// Callback to quote identifiers
$quote_ident = array($db, 'quote_identifier');
// Start a selection query
$query = 'SELECT ';
if ($this->_distinct === TRUE) {
// Select only unique results
$query .= 'DISTINCT ';
}
if (empty($this->_select)) {
// Select all columns
$query .= '*';
} else {
// Select all columns
$query .= implode(', ', array_map($quote_ident, $this->_select));
}
if (!empty($this->_from)) {
// Set tables to select from
$query .= ' FROM ' . implode(', ', array_map(array($db, 'quote_table'), $this->_from));
}
if (!empty($this->_join)) {
// Add tables to join
$query .= ' ' . Database_Query_Builder::compile_join($db, $this->_join);
}
if (!empty($this->_where)) {
// Add selection conditions
$query .= ' WHERE ' . Database_Query_Builder::compile_conditions($db, $this->_where);
}
if (!empty($this->_group_by)) {
// Add sorting
$query .= ' GROUP BY ' . implode(', ', array_map($quote_ident, $this->_group_by));
}
if (!empty($this->_having)) {
// Add filtering conditions
$query .= ' HAVING ' . Database_Query_Builder::compile_conditions($db, $this->_having);
}
if (!empty($this->_order_by)) {
// Add sorting
$query .= ' ' . Database_Query_Builder::compile_order_by($db, $this->_order_by);
}
if ($this->_limit !== NULL) {
// Add limiting
$query .= ' LIMIT ' . $this->_limit;
}
if ($this->_offset !== NULL) {
// Add offsets
$query .= ' OFFSET ' . $this->_offset;
}
return $query;
}