mysql - 如何根据时间戳查询每条记录的索引

Question

我有一个订单表，我想索引每个公司的第一个第二个第三个......等订单。

表格示例:

|---------------------|--------------------------|
|      company_id     |     created_at           |
|---------------------|--------------------------|
|          1          |   2019-01-01 01:00:00    |
|---------------------|--------------------------|
|          1          |   2019-02-01 01:00:00    |
|---------------------|--------------------------|
|          2          |   2019-03-01 02:00:00    |
|---------------------|--------------------------|
|          3          |   2019-03-01 08:30:00    |
|---------------------|--------------------------|
|          2          |   2019-03-01 10:00:00    |
|---------------------|--------------------------|

我最后会不会被这样查询。但我不知道如何......我继续返回对字段进行计数和分组，但我似乎无法根据时间戳获得每行的总和

|---------------------|--------------------------|-------|
|      company_id     |     created_at           |count()|
|---------------------|--------------------------|--------
|          1          |   2019-01-01 01:00:00    |   1   |
|---------------------|--------------------------|--------
|          1          |   2019-02-01 01:00:00    |   2   |
|---------------------|--------------------------|--------
|          2          |   2019-03-01 02:00:00    |   1   |
|---------------------|--------------------------|--------
|          3          |   2019-03-01 08:30:00    |   1   |
|---------------------|--------------------------|--------
|          2          |   2019-03-01 10:00:00    |   2   |
|---------------------|--------------------------|--------

Answer 1

SELECT 
    @row_number:=CASE
        WHEN @company_id = company_id THEN @row_number + 1
        ELSE 1
    END AS count1,
    @company_id:=company_id as company_id,
    created_at
FROM
    Table1,(SELECT @company_id:=0,@row_number:=0) as t
ORDER BY company_id;

SQL Fiddle