Question

我有一个交易表，记录每个添加到或的金额</ em>从客户余额中扣除，并带有新余额：

+----+------------+------------+--------+---------+ | id | customerId | timestamp | amount | balance | +----+------------+------------+--------+---------+ | 1 | 1 | 1000000001 | 10 | 10 | | 2 | 1 | 1000000002 | -20 | -10 | | 3 | 1 | 1000000003 | -10 | -20 | | 4 | 2 | 1000000004 | -5 | -5 | | 5 | 2 | 1000000005 | -5 | -10 | | 6 | 2 | 1000000006 | 10 | 0 | | 7 | 3 | 1000000007 | -5 | -5 | | 8 | 3 | 1000000008 | 10 | 5 | | 9 | 3 | 1000000009 | 10 | 15 | | 10 | 4 | 1000000010 | 5 | 5 | +----+------------+------------+--------+---------+

Customer表存储当前余额，如下所示：

+----+---------+ | id | balance | +----+---------+ | 1 | -20 | | 2 | 0 | | 3 | 15 | | 4 | 5 | +----+---------+

我想添加一个balanceSignSince列，用于存储余额标志上次更改的时间戳。过渡到正，否定或零计为余额变化。

更新后，根据以上数据，Customer表应包含：

+----+---------+------------------+ | id | balance | balanceSignSince | +----+---------+------------------+ | 1 | -20 | 1000000002 | | 2 | 0 | 1000000006 | | 3 | 15 | 1000000008 | | 4 | 5 | 1000000010 | +----+---------+------------------+

如何编写一个SQL查询，根据事务表格，在上次更改余额符号时更新每个客户？

我怀疑在没有相当复杂的存储过程的情况下我无法做到这一点，但我很想知道是否有任何聪明的想法出现。

Answer 1

更新了答案，但需要对现有数据进行处理

以下查询应适用于大多数情况，客户只有一个交易或没有更改符号时仍然存在问题。由于这是一次性更新，我将运行下面的查询，然后对没有设置时间戳的所有用户进行简单更新，对于它们，它将是第一个事务的时间戳：

# Find the smallest timestamp, e.g. the  
# transaction which changed the signum.
SELECT
    p.customerId as customerId,
    MIN(t.timestamp) as balanceSignSince
FROM
    transaction as t,
    (
      # find the latest timestamp having
      # a different sign for each user.
      # Here is the issue with users having
      # only a single transaction or no sign
      # changes.
      SELECT 
        u.customerId as customerId,
        MAX(t.timestamp) as balanceSignSince
      FROM
        transaction as t,
        customer as c,
        (
          # find the timestamp of the very last 
          # transaction for every user.
          SELECT 
            t.customerId as customerId,
            MAX(t.timestamp) as lastTransaction            
          FROM
            transaction as t
          GROUP BY 
            t.customerId
        ) as u
        WHERE
          u.customerId = c.id
          AND u.customerId = t.customerId
          AND SIGN(c.balance) <> SIGN(t.balance)
      GROUP BY
        u.customerId
    ) as p
WHERE 
    p.customerId = t.customerId
    AND p.balanceSignSince < t.timestamp
GROUP BY
    p.customerId;

小提琴：http://sqlfiddle.com/#!9/bd0760/13

原始答案

这应该可以获得符号更改的时间戳：

SELECT 
    c.id as id,
    MAX(t.timestamp) as balanceSignSince 
FROM 
    transaction as t, 
    customer as c
WHERE
    t.customerId = c.id
    AND SIGN(t.balance) <> SIGN(c.balance)

这需要在使用新余额更新客户表之前执行。如果您有转换触发器：插入您应该将上述内容放入更新客户表的查询中。

Answer 2

这使用模拟的rank（）函数。

select customerId, min(tstamp) from
(
select tstamp,
       if (@cust = customerId and sign(@bal) = sign(balance), @rn := @rn,
           if (@cust = customerId and sign(@bal) <> sign(balance), @rn := @rn + 1, @rn := 0)) as rn,
       @cust := customerId as customerId, @bal := balance as balance
from
      (select @rn := 0) x,
      (select id, @cust := customerId as customerId, tstamp, amount, @bal := balance as balance 
       from trans order by customerId, tstamp desc) y
) z
where rn = 0
group by customerId;

检查：http://rextester.com/XJVKK61181

此脚本返回如下表格：

+------------+----+------------+---------+
| tstamp     | rn | customerId | balance |
+------------+----+------------+---------+
| 1000000003 | 0  | 1          | -20     |
| 1000000002 | 0  | 1          | -10     |
| 1000000001 | 1  | 1          | 10      |
| 1000000006 | 0  | 2          | 0       |
| 1000000005 | 2  | 2          | -10     |
| 1000000004 | 2  | 2          | -5      |
| 1000000009 | 0  | 3          | 15      |
| 1000000008 | 2  | 3          | 5       |
| 1000000007 | 3  | 3          | -5      |
| 1000000010 | 0  | 4          | 5       |
+------------+----+------------+---------+

然后选择文件的最小值（时间戳），其中rn = 0：

+------------+-------------+
| customerId | min(tstamp) |
+------------+-------------+
| 1          | 1000000002  |
+------------+-------------+
| 2          | 1000000006  |
+------------+-------------+
| 3          | 1000000009  |
+------------+-------------+
| 4          | 1000000010  |
+------------+-------------+

在（我的）SQL中获取上次余额符号更改

2 个答案: