返回第一个日期和以前的日期

Question

一个监护人有3个约会。

我想返回第一个日期，然后返回它的前一个日期。

数据应类似于：

custid first       previous
11     2019-06-10  2019-06-15
11     2019-06-10  2019-07-10

我已经做完了，但是无法将其放在第二行。

SELECT A.PersonID ,min(a.date) as first,b.date as previous,c.date as previous from Persons as a
INNER JOIN (select PersonID ,date from Persons) b
on a.PersonID
=b.PersonID  AND 
a.date<
b.date
INNER JOIN (select PersonID ,date from Persons) c
            on b.PersonID=
c.PersonID
           AND b.date<
c.date

我得到的输出：

personid first         previous          previous
11       2019-06-10    2019-06-15            2019-07-10

我希望它看起来像：

custid first       previous
11     2019-06-10  2019-06-15
11     2019-06-10  2019-07-10

Answer 1

您不需要添加第三个内部联接表。由于您将min（）与其他列一起使用，因此应伴随Group By。

select
  a.PersonID as custid,
  min(a.date) as first,
  b.date as previous     
from
  Persons as a
inner join Persons b on a.PersonID = b.PersonID and b.date > a.date
group by a.PersonID, b.date