Question

由于mysql查询，我有此表：

orders | customer |
1      | A        |
1      | A        |
1      | B        |
1      | B        |
1      | B        |

仅使用mysql，我需要为每个客户创建一个索引索引发生的列以获取此表：

orders | customer | index
1      | A        | 1
1      | A        | 2
1      | B        | 1
1      | B        | 2
1      | B        | 3

我尝试使用它：

set @i=1;
while @i<99999 do
  select 
    count(order_id) as 'orders',
    customer_id as 'customer',
    @i as 'index'
  from
    orders
  set @i= @i+1;     
end while;

但是我得到一个陈述错误。抱歉，我不知道该怎么做。任何想法将不胜感激。

Answer 1

在MySQL 8.0上执行此操作的标准方法是使用窗口功能：

SELECT orders, customer, 
  ROW_NUMBER() OVER (PARTITION BY customer) AS `index`
FROM orders

在MySQL 8.0之前，您可以使用内联用户变量来完成技巧。

SET @i = 0, @c = '';

SELECT 
  orders, 
  IF(@c=customer, @i:=@i+1, @i:=1) AS `index`, 
  @c:=customer AS customer
FROM orders
ORDER BY customer;

不幸的是，这需要customer列位于index列之后。

Answer 2

SELECT 
    orders.* , 
    customerOrderCount , 
    IF(@i > 1, @i:= @i - 1, @i:=customerOrdercount) AS orderIndex
FROM (SELECT * FROM orders ORDER BY customer ASC ) AS orders
    JOIN (SELECT customer, count(*) AS customerOrderCount FROM orders GROUP BY 
customer) counts USING (customer)
ORDER BY customer ASC, orderIndex;

MySQL如何在SELECT中生成行索引（行）？

2 个答案: