Quote aliased field names.

Aliased fields need to be quoted for postgres to properly return the
names in the result sets. Without quoting names are returned as
lowercase version. An alternative workaround would be to snake_case
aliases and inflect them back when building results.

lib/Cake/Database/Query.php

@@ -410,12 +410,13 @@ public function distinct($on = [], $overwrite = false) {
  * @return string
  */
 	protected function _buildSelectPart($parts) {
+		$driver = $this->_connection->driver();
 		$select = 'SELECT %s%s';
 		$distinct = null;
 		$normalized = [];
 		foreach ($parts as $k => $p) {
 			if (!is_numeric($k)) {
-				$p = $p . ' AS ' . $k;
+				$p = $p . ' AS ' . $driver->quoteIdentifier($k);
 			}
 			$normalized[] = $p;
 		}