Updated UPGRADE.md for 3.x

UPGRADE.md

@@ -1,3 +1,35 @@
+# Upgrade to DEVELOP
+
+## BC BREAK: the PDO symbols are no longer part of the DBAL API
+
+1. The support of `PDO::PARAM_*`, `PDO::FETCH_*`, `PDO::CASE_*` and `PDO::PARAM_INPUT_OUTPUT` constants in the DBAL API is removed.
+2. `\Doctrine\DBAL\Driver\PDOStatement` does not extend `\PDOStatement` anymore.
+
+Before:
+
+    use Doctrine\DBAL\Portability\Connection;
+
+    $params = array(
+        'wrapperClass' => Connection::class,
+        'fetch_case' => PDO::CASE_LOWER,
+    );
+
+    $stmt->bindValue(1, 1, PDO::PARAM_INT);
+    $stmt->fetchAll(PDO::FETCH_COLUMN);
+
+After:
+
+    use Doctrine\DBAL\Driver\Statement;
+    use Doctrine\DBAL\Portability\Connection;
+
+    $params = array(
+        'wrapperClass' => Connection::class,
+        'fetch_case' => Connection::CASE_LOWER,
+    );
+
+    $stmt->bindValue(1, 1, Statement::PARAM_INT);
+    $stmt->fetchAll(Statement::FETCH_COLUMN);
+
 # Upgrade to UNRELEASED
 
 ## DEPRECATION: direct usage of the PDO APIs in the DBAL API