如何增量计算重复实例的数量

Question

我想递增地计算 table 中重复实例的数量，所以如果我有这样的 table：

id   | name  | status |
-----------------------
1    | John  |    1   | 
2    | Jane  |    1   |
4    | John  |    1   |
5    | John  |    1   |
6    | Jane  |    1   |
7    | John  |    1   |

使用“名称”列作为参考，输出将是

id   | name  | status | count |
------------------------------
1    | John  |    1   |   1   |
2    | Jane  |    1   |   1   |
4    | John  |    1   |   2   |
5    | John  |    1   |   3   |
6    | Jane  |    1   |   2   |
7    | John  |    1   |   4   |

DBMS 实现是 MySQL，版本 5.6

Answer 1

只需使用row_number():

select t.*, row_number() over (partition by name order by id) as count
from t
order by id;

Answer 2

SELECT t1.id, t1.name, t1.status, COUNT(*) `count`
FROM tablename t1
JOIN tablename t2 USING (name)
WHERE t1.id >= t2.id
GROUP BY t1.id, t1.name, t1.status
ORDER BY t1.id

Answer 3

在MySQL5.x中，window函数不可用，一个选项使用相关子查询：

select t.*,
    (
        select count(*)
        from mytable t1
        where t1.name = t.name and t1.id <= t.id
    ) rn
from mytable t

您也可以使用用户变量执行此操作：

select t.*,
    case when @name = (@name := name)
        then @rn := @rn + 1
        else @rn := 1
    end as rn
from (select * from mytable order by name, id) t
cross join (select @name := null, @rn := 0) x

这两种方法各有利弊。对于大型数据集，第二个解决方案比第一个更好地扩展，但是用户变量在 MySQL 中很棘手，现在正式计划在未来的版本中弃用。

如何增量计算重复实例的数量

How to incrementally count the number of repeated instances

mysql

sql

subquery

window-functions

mysql-5.6