聚合查询

统计（COUNT）

$num = User::where(['type' => 1])->count()

求和（SUM）

User::where(['type' => 1])->sum('balance')

平均值

User::where(['type' => 1])->avg('balance')

最大值

User::where(['type' => 1])->max('balance')

最小值

User::where(['type' => 1])->min('balance')