// 方式一：字符串键
M("order")->where(array(
    "status" => 1,
    "_complex" => array("or",
        array("amount" => array(">", 1000)),
        array("vip_level" => array(">=", 3)),
    ),
))->select();
// WHERE (`status` = :w0 AND (`amount` > :w1 OR `vip_level` >= :w2))

// 方式二：数字首元素
M("order")->where(array(
    array("_complex", "or", array("a" => 1), array("b" => 2)),
))->select();

M("user")->where(array(
    "name|email" => "张",   // name=张 OR email=张
))->select();

// 等价
M("user")->where(array(
    "_complex" => array("or", array("name" => "张"), array("email" => "张")),
))->select();