突然发现的问题
简单举个例子
$assignment=Db::name('assignment');//赋值给变量，本意是想后面调用方便

$map=[['assign_user','eq','jason222'],['delete_time','eq',0]];

$assign_list = $assignment->where($map)->all();
//重新对查询条件赋值
$map=[['assign_user','eq','jason3333'],['delete_time','eq',0]];

$assign_list = $assignment->where($map)->all();

echo $assignment->getLastSql();

//打印的结果
SELECT * FROM `sky_assignment` WHERE
`assign_user` = 'jason222' AND `delete_time` = 0 AND
`assign_user` = 'jason3333' AND `delete_time` = 0
第二次虽然重新对$map赋值，但是生成的查询语句还是携带了第一次的查询条件
难道每次数据操作都要重新写Db::name()吗