- A lot of fixes made again in this patch

src/QueryBuilder.php

@@ -351,6 +351,30 @@ class QueryBuilder implements Query\QueryBuilderInterface
         return $this;
     }
 
+    public function alter(array $fieldlist, string $table, ? string $database = null, ? string $schema = null) : self
+    {
+        if ( null === $this->getFragment(Query\Create::class) ) {
+            if ( $schema ) {
+                $table = "$schema.$table";
+            }
+
+            if ( $database ) {
+                $table = "$database.$table";
+            }
+
+            $alter = new Query\Alter();
+            $this->push($alter);
+
+            $alter->fieldList = $fieldlist;
+            $alter->table = $table;
+        }
+        else {
+            throw new \Exception("A create SQL fragment was already found within the query builder");
+        }
+
+        return $this;
+    }
+
     public function engine(string $value) : self
     {
         if ( null === $engine = $this->getFragment(Query\Engine::class) ) {
@@ -413,13 +437,22 @@ class QueryBuilder implements Query\QueryBuilderInterface
         return null;
     }
 
-    public function removeFragment(Query\Fragment $fragment) : void
+    public function removeFragment(/*Query\Fragment|array*/ $fragment) : void
     {
+        is_object($fragment) && $fragment = get_class($fragment);
+
         foreach($this->queryStack as $key => $item) {
-            if ( $item === $fragment ) {
+            if ( get_class($item) === $fragment ) {
                 unset($this->queryStack[$key]);
             }
         }
+
+        if ( $fragment === Query\Where::class ) {
+            unset($this->where);
+        }
+        elseif ( $fragment === Query\Having::class ) {
+            unset($this->having);
+        }
     }
 
     public function getFragments() : array