It's either a Query Builder or MySQL bug. I just ran into it. Union wraps everything in parenthesis, and MySql doesn't like it.

This is what the Builder produces:

( SELECT... ) UNION ( ( SELECT... ) UNION ( SELECT... ) )

This is what is should produce:

( SELECT... ) UNION ( SELECT... ) UNION ( SELECT... )

I fixed it by modifying \Illuminate\Database\Query\Grammers\MysqlGrammar::compileUnion

protected function compileUnion(array $union)
{
	$joiner = $union['all'] ? ' union all ' : ' union ';
	$sql     = $union['query']->toSql();

	return $joiner.(preg_match( '/^\(.*\)$/', $sql ) ? $sql : "($sql)" );
}