Question

我有一个像这样的表mysql：

        static void Main(string[] args)
    {
        bool exit = false;
        List<float> grades = new List<float>();

        do
        {
            Console.WriteLine("1. Enter Grades");
            Console.WriteLine("2. Get Average");
            Console.WriteLine("3. My program");
            Console.WriteLine("4. exit");
            Console.WriteLine("");

            string input = Console.ReadLine();

            Console.WriteLine("");

            if (input == "1")
            {
                int totalGrades = 0;

                //User Input
                Console.WriteLine("How many grades do you want to enter? ");
                while (true)
                {
                    try
                    {
                        totalGrades = Convert.ToInt32(Console.ReadLine());
                        break;
                    }
                    catch (FormatException)
                    {
                        Console.WriteLine("This is not a valid number");
                        continue;
                    }
                }
                Console.WriteLine("");

                while (totalGrades > 0)
                {
                    while (true)
                    {
                        try
                        {
                            grades.Add(Convert.ToInt32(Console.ReadLine()));
                            totalGrades--;
                            break;
                        }
                        catch (FormatException)
                        {
                            Console.WriteLine("This is not a valid number");
                            continue;
                        }
                    }
                }

                Console.WriteLine("");
            }
            else if (input == "2")
            {

                double average = grades.Average();

                if (average >= 90)
                {
                    Console.WriteLine($"The average is a {average} which is an A.");
                }
                else if (average >= 80)
                {
                    Console.WriteLine($"The average is a {average} which is an B.");
                }
                else if (average >= 70)
                {
                    Console.WriteLine($"The average is a {average} which is an C.");
                }
                else if (average >= 60)
                {
                    Console.WriteLine($"The average is a {average} which is an D.");
                }
                else
                {
                    Console.WriteLine($"The average is a {average} which is an E.");
                }

                Console.WriteLine("");

            }
            else if (input == "4")
            {
                exit = true;
            } else
            {
                Console.WriteLine("This is not an option");
            }
        }
        while (exit == false);
    }

对于每个工厂，我试图从最新的“ date_op”中选择具有最大“线”的行。所以从这个：

CREATE TABLE prelevement (
  line int,
  facture varchar(30),
  date_op varchar(30),
  code_op varchar(30)
);

        insert into prelevement 
(line,facture,date_op,code_op)
values 
(1,'F1','2019-02-20','PREL'),
(2,'F1','2019-02-20','CART'),
(3,'F1','2019-02-20','REJE'),
(8,'F1','2019-02-19','PREL'),
(2,'F2','2019-02-15','PREL'),
(1,'F2','2017-01-25','PREL'),
(1,'F3','2018-02-25','REJ'),
(2,'F3','2018-02-25','CART');

我正在尝试获得以下结果：

| line | facture | date_op    | code_op |
| ---- | ------- | ---------- | ------- |
| 1    | F1      | 2019-02-20 | PREL    |
| 2    | F1      | 2019-02-20 | CART    |
| 3    | F1      | 2019-02-20 | REJE    |
| 8    | F1      | 2019-02-19 | PREL    |
| 2    | F2      | 2019-02-15 | PREL    |
| 1    | F2      | 2017-01-25 | PREL    |
| 1    | F3      | 2018-02-25 | REJ     |
| 2    | F3      | 2018-02-25 | CART    |

我来过这里，但是我不确定从这里去哪里：

| line | facture | date_op    | code_op |
| ---- | ------- | ---------- | ------- |
| 3    | F1      | 2019-02-20 | REJE    |
| 2    | F2      | 2019-02-15 | PREL    |
| 2    | F3      | 2018-02-25 | CART    |

Answer 1

在MySQL中，您可以使用：

select p.*
from prelevement p
where (date_op, line) = (select date_op, line
                         from prelevement p2
                         where p2.facture = p.facture
                         order by date_op desc, line desc
                         limit 1
                        );

您还可以通过两个相关的子查询来执行此操作：

select p.*
from prelevement p
where p.date_op = (select max(p2.date_op)
                   from prelevement p2
                   where p2.facture = p.facture
                  ) and
     p.line = (select max(p2.line)
               from prelevement p2
               where p2.facture = p.facture and p2.date_op = p.date_op
              ) ;

在MySQL 8.0中，您可以使用窗口函数：

select p.*
from (select p.*, row_number() over (partition by facture order by date_op desc, line desc) as seqnum
      from prelevement p
     ) p
where seqnum = 1;

Here是所有三种解决方案的db <>小提琴。

Answer 2

这将起作用：

CREATE TABLE prelevement (
  line int,
  facture varchar(30),
  date_op varchar(30),
  code_op varchar(30)
);

✓

        insert into prelevement 
(line,facture,date_op,code_op)
values 
(1,'F1','2019-02-20','PREL'),
(2,'F1','2019-02-20','CART'),
(3,'F1','2019-02-20','REJE'),
(8,'F1','2019-02-19','PREL'),
(2,'F2','2019-02-15','PREL'),
(1,'F2','2017-01-25','PREL'),
(1,'F3','2018-02-25','REJ'),
(2,'F3','2018-02-25','CART');

✓

select * from prelevement pp where facture in 
(
  select facture from (
    select * from prelevement p 
    where facture in ( 
      select facture from prelevement pin 
      group by facture
      having max(pin.date_op) = p.date_op 
    )
  ) t
  group by facture
  having max(t.line) = pp.line
)

line | facture | date_op    | code_op
---: | :------ | :--------- | :------
   3 | F1      | 2019-02-20 | REJE   
   2 | F2      | 2019-02-15 | PREL   
   2 | F3      | 2018-02-25 | CART

db <>提琴here

如何选择最大值为2列的行

2 个答案: