[solved] data duplication or data loss after laravel paginate() paging

【 resolved 】Laravel paginate() After paging Duplicate data or Data loss problem

Problem scenario description ：

1. It is known that there is a student table and a consumption points table . Now the student table is arranged in positive order according to the consumption points of each student （ That is, the integral is arranged from high to low ）.
2. Student list students And Consumption points table orders The table is a one to many relationship （ A piece of student data Corresponding Multiple voting points data ）.

Examples of data tables

Student list （students）

id	name（ Student name ）
1	Balsam pear
2	Washbasin King
3	Old stick

Consumption points table （orders）

id	vote（ vote ）	students_id（ Student list id）	is_pay（ Whether to pay ）
1	2	1	1
2	3	3	1
3	4	1	0
4	5	2	1
5	2	1	1
6	1	2	1
7	3	2	1
8	2	1	1
9	6	3	1

Error code example

At this point, the acquired data is used by the front end laravel Own paging $data->links(); Data loss will occur Or data duplication

public function studentList(Request $request){
    
		// Get a list of students 
        $data = Student::select('students.*',DB::raw('(SELECT SUM(contribution_value) FROM orders WHERE orders.students_id = students.id and orders.is_pay = 1) as sum_contribution_value'))
        ->orderBy('sum_contribution_value','desc')
        ->paginate(10);
        return view('h5.student.studentList',compact('data'));
    }

Example of rendered error data ：

Solution ：

Examples of correct code ：

public function studentList(Request $request){
    
		// Get a list of students 
        $data = Student::select('students.*',DB::raw('(SELECT SUM(contribution_value) FROM orders WHERE orders.students_id = students.id and orders.is_pay = 1) as sum_contribution_value'))
        ->orderBy('sum_contribution_value','desc')
        >orderBy('students.id','desc')// Add this line of code .order by Because sorting is not unique , So the order of each query is different , The data segment intercepted by paging may have duplicate data or cause data loss 
        ->paginate(10);
        return view('h5.student.studentList',compact('data'));
    }

Return the reason why the data is lost or duplicated

As shown in the error code example above ：->orderBy('sum_contribution_value','desc') Only this identifier is used for sorting , However, this representation is not a unique identifier for the entire returned data ！
Mysql Use order by When sorting, the sorting ID is not unique , So the order of each query is different , The data segment intercepted by paging may have duplicate data or cause data loss .
Therefore, it is sufficient to add a unique identification field for sorting （ For example, the uniqueness of a table id Or fields with unique constraints such as order number ）.