laravel 查询构造器2

//查询构造器
    public function query()
    {
        //获取所有的数据
        $student = DB::table('student')->get();
        var_dump($student);

        //获取一条数据
        $student = DB::table('student')->first();
        var_dump($student);

        //使用where获取数据
        $student = DB::table('student')->where('id','>=',12)->get();
        var_dump($student);

        //使用多个where条件获取数据
        $student = DB::table('student')
            ->whereRaw('id>=? and age > 10',[2,18])
            ->get();
        var_dump($student);

        //pluck返回结果集中指定的字段,列数据
        $student = DB::table('student')
            ->whereRaw('id>=? and age > 10',[2,18])
            ->pluck('name');
        var_dump($student);

        //lists,返回结果
        $student = DB::table('student')
            ->whereRaw('id>=? and age > 10',[2,18])
            ->lists('name','id');//id作为下标，name作为值
        var_dump($student);

        //select获取指定的字段
        $student = DB::table('student')
            ->whereRaw('id>=? and age > 10',[2,18])
            ->select('id','name','age')
            ->get();
        var_dump($student);

        //chunk,分次查询，查询量过大的时候使用
        DB::table('student')->chunk(1000,function($students){
            var_dump($students);//每次查询1000条
//            if(条件满足){
//                return false;//跳出查询
//            }
        });

        //查询中的聚合函数
        //count() avg() max() sum() min()
        $count = DB::table('student')->count();
        $avg = DB::table('student')->avg('age');
        $max = DB::table('student')->max('age');
        $min = DB::table('student')->min('age');
        $sum = DB::table('student')->sum('age');

    }