Question

假设我有以下数据：

.mdf

我正在尝试获取CUSTOMER_ID CONTACT_ID COMM_CREATION_DAY DAYS_SINCE_LAST_CONTACT 10000 28036173295 2014-12-21 0 10000 28365672745 2015-01-29 DATEDIFF('2015-01-29','2014-12-21') 10000 28576719155 2015-02-26 DATEDIFF('2015-02-26','2014-01-29') 38409 28432217395 2015-02-07 0 38409 28565986955 2015-02-25 DATEDIFF('2015-02-25,'2015-02-07')列，但MySQL中没有DAYS_SINCE_LAST_CONTACT或LEAD函数。如何在一个LAG语句中执行此操作？

我尝试了以下内容：

SELECT

但那给了我：

SELECT CUSTOMER_ID, COMM_ID , COMM_CREATION_DAY, PREVIOUS_COMM_CREATION_DAY FROM 
(
select
c.*
, @prev AS PREVIOUS_COMM_CREATION_DAY
, @prev := COMM_CREATION_DAY
FROM contacts c, (select @prev:=NULL) vars
ORDER BY CUSTOMER_ID, c.COMM_CREATION_DAY, c.COMM_ID
) sq
ORDER BY CUSTOMER_ID, COMM_CREATION_DAY

CUSTOMER_ID CONTACT_ID COMM_CREATION_DAY LAST_CONTACT_DATE 10000 28036173295 2014-12-21 NULL 10000 28365672745 2015-01-29 2014-12-21 10000 28576719155 2015-02-26 2015-01-29 38409 28432217395 2015-02-07 2015-02-26 (THIS IS INCORRECT!) 38409 28565986955 2015-02-25 2015-02-07在所有情况下都没有正确显示最后一列。

有什么想法吗？

Answer 1

是的，在mysql中你需要使用用户定义的变量来进行这样的计算

select
customer_id,
contact_id,
contact_date,
DAYS_SINCE_LAST_CONTACT 
from(
  select
  customer_id,
  contact_id,
  contact_date,
  @diff:= if(@prev_customer = customer_id,datediff(contact_date,@prev_date),0) as DAYS_SINCE_LAST_CONTACT,
  @prev_customer:=customer_id,
  @prev_date:= contact_date
  from customer c,(select @prev_customer:=0,@prev_date:=null)x
  order by customer_id,contact_date
)x

http://sqlfiddle.com/#!9/6cb9f/2

MySQL滞后列DATEDIFF

1 个答案: