SQL将行数据分组为一行

Question

我在这样的表中有数据：

我要整理表格数据，以便每行最多可以得到3个字母（按帐号分组）。

以下是我想要的结果：

我可以使用密集排名对帐号进行分组，但是不确定如何以上述格式获取我想要的数据。

逻辑： 帐户123有4个字母。最终结果按帐号（前3个字母）分组，因为每行最多只能有3个字母。第四个字母必须在第二行。

Answer 1

这里有一个使用conditional aggregation的选项，首先创建一个row_number，然后使用%（模运算符）每3行创建一个行分组：

select account_number, 
       max(case when rn % 3 = 1 then letter end) as letter1,
       max(case when rn % 3 = 2 then letter end) as letter2,
       max(case when rn % 3 = 0 then letter end) as letter3
from (
    select *, row_number() over (partition by account_number, rn % 3 order by rn) newrn
    from (
       select *, row_number() over (partition by account_number order by letter) rn
        from yourtable 
        ) t
    ) y
group by account_number, newrn
order by account_number

• Online Demo

Answer 2

我只需要打一次row_number()：

select account_number,
       max(case when seqnum % 3 = 1 then letter end) as letter_a,
       max(case when seqnum % 3 = 2 then letter end) as letter_b,
       max(case when seqnum % 3 = 0 then letter end) as letter_c
from (select t.*,
             row_number() over (partition by account_number order by letter) as seqnum
      from t
     ) t
group by account_number, floor( (seqnum - 1) / 3)
order by account_number, min(seqnum);