Add compileExists grammar

Author: cooperl22

src/Query/Grammars/DB2Grammar.php

@@ -179,6 +179,21 @@ protected function compileOffset(Builder $query, $offset)
         return '';
     }
 
+    /**
+     * Compile an exists statement into SQL.
+     *
+     * @param  \Illuminate\Database\Query\Builder  $query
+     * @return string
+     */
+    public function compileExists(Builder $query)
+    {
+        $existsQuery = clone $query;
+
+        $existsQuery->columns = [];
+
+        return $this->compileSelect($existsQuery->selectRaw('1')->limit(1));
+    }
+
     /**
      * Get the format for database stored dates.
      *