Implement subquery support in joins

Author: avbdr

MysqliDb.php

@@ -117,7 +117,7 @@ public function __construct($host = NULL, $username = NULL, $password = NULL, $d
         else
             $this->port = $port;
 
-        if ($host == null && $username == null && $db == null) {
+        if ($username == null && $db == null) {
             $this->isSubQuery = true;
             return;
         }
@@ -427,12 +427,14 @@ public function join($joinTable, $joinCondition, $joinType = '')
      {
         $allowedTypes = array('LEFT', 'RIGHT', 'OUTER', 'INNER', 'LEFT OUTER', 'RIGHT OUTER');
         $joinType = strtoupper (trim ($joinType));
-        $joinTable = filter_var($joinTable, FILTER_SANITIZE_STRING);
 
         if ($joinType && !in_array ($joinType, $allowedTypes))
             die ('Wrong JOIN type: '.$joinType);
 
-        $this->_join[$joinType . " JOIN " . self::$_prefix . $joinTable] = $joinCondition;
+        if (!is_object ($joinTable))
+            $joinTable = self::$_prefix . filter_var($joinTable, FILTER_SANITIZE_STRING);
+
+        $this->_join[] = Array ($joinType,  $joinTable, $joinCondition);
 
         return $this;
     }
@@ -587,7 +589,7 @@ protected function _buildPair ($operator, $value) {
         $subQuery = $value->getSubQuery ();
         $this->_bindParams ($subQuery['params']);
 
-        return " " . $operator . " (" . $subQuery['query'] . ")";
+        return " " . $operator . " (" . $subQuery['query'] . ") " . $subQuery['alias'];
     }
 
     /**
@@ -679,8 +681,16 @@ protected function _buildJoin () {
         if (empty ($this->_join))
             return;
 
-        foreach ($this->_join as $prop => $value)
-            $this->_query .= " " . $prop . " on " . $value;
+        foreach ($this->_join as $data) {
+            list ($joinType,  $joinTable, $joinCondition) = $data;
+
+            if (is_object ($joinTable))
+                $joinStr = $this->_buildPair ("", $joinTable);
+            else
+                $joinStr = $joinTable;
+
+            $this->_query .= " " . $joinType. " JOIN " . $joinStr ." on " . $joinCondition;
+        }
     }
 
     /**
@@ -946,7 +956,8 @@ public function getSubQuery () {
 
         array_shift ($this->_bindParams);
         $val = Array ('query' => $this->_query,
-                      'params' => $this->_bindParams
+                      'params' => $this->_bindParams,
+                      'alias' => $this->host
                 );
         $this->reset();
         return $val;
@@ -1031,9 +1042,9 @@ public function func ($expr, $bindParams = null) {
     /**
      * Method creates new mysqlidb object for a subquery generation
      */
-    public static function subQuery()
+    public static function subQuery($subQueryAlias = "")
     {
-        return new MysqliDb();
+        return new MysqliDb ($subQueryAlias);
     }
 
     /**

readme.md

@@ -307,6 +307,20 @@ echo "total records found: " . $cnt;
 ```
 
 ### Subqueries
+Subquery init
+
+Subquery init without an alias to use in inserts/updates/where Eg. (select * from users)
+```php
+$sq = $db->subQuery();
+$sq->get ("users");
+```
+ 
+A subquery with an alias specified to use in JOINs . Eg. (select * from users) sq
+```php
+$sq = $db->subQuery("sq");
+$sq->get ("users");
+```
+
 Subquery in selects:
 ```php
 $ids = $db->subQuery ();
@@ -333,6 +347,18 @@ $id = $db->insert ("products", $data);
 // Gives INSERT INTO PRODUCTS (productName, userId, lastUpdated) values ("test product", (SELECT name FROM users WHERE id = 6), NOW());
 ```
 
+Subquery in joins:
+```php
+$usersQ = $db->subQuery ("u");
+$usersQ->where ("active", 1);
+$usersQ->get ("users");
+
+$db->join($usersQ, "p.userId=u.id", "LEFT");
+$products = $db->get ("products p", null, "u.login, p.productName");
+print_r ($products);
+// SELECT u.login, p.productName FROM products p LEFT JOIN (SELECT * FROM t_users WHERE active = 1) u on p.userId=u.id;
+```
+
 ###EXISTS / NOT EXISTS condition
 ```php
 $sub = $db->subQuery();

tests.php

@@ -292,6 +292,23 @@ function createTable ($name, $data) {
     echo "Invalid select result with subquery";
     exit;
 }
+
+
+$usersQ = $db->subQuery ("u");
+$usersQ->where ("active", 1);
+$usersQ->get("users");
+
+$db->join($usersQ, "p.userId=u.id", "LEFT");
+$products = $db->get ("products p", null, "u.login, p.productName");
+if ($products[2]['login'] != 'user1' || $products[2]['productName'] != 'product3') {
+    echo "invalid join with subquery";
+    exit;
+}
+if ($db->count != 5) {
+    echo "invalid join with subquery count";
+    exit;
+}
+
 //TODO: insert test
 $db->delete("users");
 $db->get("users");