Add support for DISTINCT clause

docs/en/reference/query-builder.rst

@@ -87,6 +87,21 @@ and ``delete($tableName)``:
 You can convert a query builder to its SQL string representation
 by calling ``$queryBuilder->getSQL()`` or casting the object to string.
 
+DISTINCT-Clause
+~~~~~~~~~~~~~~~
+
+The ``SELECT`` statement can be specified with a ``DISTINCT`` clause:
+
+.. code-block:: php
+
+    <?php
+
+    $queryBuilder
+        ->select('name')
+        ->distinct()
+        ->from('users')
+    ;
+
 WHERE-Clause
 ~~~~~~~~~~~~
 

lib/Doctrine/DBAL/Query/QueryBuilder.php

@@ -59,6 +59,7 @@ class QueryBuilder
      */
     private $sqlParts = [
         'select'  => [],
+        'distinct'  => false,
         'from'    => [],
         'join'    => [],
         'set'     => [],
@@ -469,6 +470,25 @@ public function select($select = null)
         return $this->add('select', $selects);
     }
 
+    /**
+     * Adds DISTINCT to the query.
+     *
+     * <code>
+     *     $qb = $conn->createQueryBuilder()
+     *         ->select('u.id')
+     *         ->distinct()
+     *         ->from('users', 'u')
+     * </code>
+     *
+     * @return $this This QueryBuilder instance.
+     */
+    public function distinct() : self
+    {
+        $this->sqlParts['distinct'] = true;
+
+        return $this;
+    }
+
     /**
      * Adds an item that is to be returned in the query result.
      *
@@ -1098,7 +1118,8 @@ public function resetQueryPart($queryPartName)
      */
     private function getSQLForSelect()
     {
-        $query = 'SELECT ' . implode(', ', $this->sqlParts['select']);
+        $query = 'SELECT ' . ($this->sqlParts['distinct'] ? 'DISTINCT ' : '') .
+                  implode(', ', $this->sqlParts['select']);
 
         $query .= ($this->sqlParts['from'] ? ' FROM ' . implode(', ', $this->getFromClauses()) : '')
             . ($this->sqlParts['where'] !== null ? ' WHERE ' . ((string) $this->sqlParts['where']) : '')

tests/Doctrine/Tests/DBAL/Query/QueryBuilderTest.php

@@ -50,6 +50,17 @@ public function testSimpleSelect() : void
         self::assertEquals('SELECT u.id FROM users u', (string) $qb);
     }
 
+    public function testSimpleSelectWithDistinct() : void
+    {
+        $qb = new QueryBuilder($this->conn);
+
+        $qb->select('u.id')
+           ->distinct()
+           ->from('users', 'u');
+
+        self::assertEquals('SELECT DISTINCT u.id FROM users u', (string) $qb);
+    }
+
     public function testSelectWithSimpleWhere() : void
     {
         $qb   = new QueryBuilder($this->conn);