问题描述
我们如何编写一个可以生成 'Sequence_Code' 的 sql 函数，如 AA,AB,AC....AZ。 BA,BB,BC.... 与每个“ID”的“Current_Year”的最后两位数字的组合。 按“Record_Date”排序
例如：如果第一行的 Current_Year 是 2019，那么 Sequence_Code 应该是 19AA。 我的表是 LoadData
| Sequence_Code | ID | Current_Year | Record_Date |
|---|---|---|---|
| NULL | 310001 | 2019 | 2019-01-01 |
| NULL | 310002 | 2018 | 2018-02-22 |
| NULL | 310003 | 2020 | 2020-02-20 |
| NULL | 310004 | 2020 | 2020-02-10 |
预期输出为：
| Sequence_Code | ID | Current_Year | Record_Date |
|---|---|---|---|
| 19AA | 310001 | 2019 | 2019-01-01 |
| 18AB | 310002 | 2018 | 2018-02-22 |
| 20AC | 310003 | 2020 | 2020-02-20 |
| 公元20年 | 310004 | 2020 | 2020-02-10 |
解决方法
最简单的方法可能是生成所有组合并枚举它们：
with alpha as (
select 'A' as alpha union all
select 'B' as alpha union all
. . . -- continue for the rest of the letters
select 'Z' as alpha
),alphas as (
select concat(a1.alpha,a2.alpha) as alpha2,row_number() over (order by a1.alpha,a2.alpha) as seqnum
from alpha a1 cross join
alpha a2
)
select current_year || alpha2.alpha2 as sequence_code,t.*
from (select t.*,row_number() over (partition by current_year order by record_date) as seqnum
from LoadData t
) t left join
alpha2
on t.seqnum = a2.seqnum;
注意：这里使用标准 SQL，因此功能可能有不同的语法，具体取决于数据库。
,使用 ROW_NUMBER() 窗口函数和数学：
WITH cte AS (SELECT *,ROW_NUMBER() OVER (ORDER BY Record_Date) rn FROM LoadData)
SELECT RIGHT(Current_Year,2) +
CHAR(ASCII('A') + rn / 26 + CASE rn % 26 WHEN 0 THEN -1 ELSE 0 END) +
CHAR(ASCII('A') - 1 + CASE rn % 26 WHEN 0 THEN 26 ELSE rn % 26 END) Sequence_Code,ID,Current_Year,Record_Date
FROM cte
ORDER BY rn
如果要更新表的 Sequence_Code 列：
WITH cte AS (SELECT *,ROW_NUMBER() OVER (ORDER BY Record_Date) rn FROM LoadData)
UPDATE cte
SET Sequence_Code = RIGHT(Current_Year,2) +
CHAR(ASCII('A') + rn / 26 + CASE rn % 26 WHEN 0 THEN -1 ELSE 0 END) +
CHAR(ASCII('A') - 1 + CASE rn % 26 WHEN 0 THEN 26 ELSE rn % 26 END)
参见demo。
结果：
> Sequence_Code | ID | Current_Year | Record_Date
> :------------ | -----: | -----------: | :----------
> 18AA | 310001 | 2018 | 2018-01-01
> 19AB | 310002 | 2019 | 2019-02-22
> 20AC | 310004 | 2020 | 2020-02-10
> 20AD | 310003 | 2020 | 2020-02-20