问题
How do i identify the first row that has value for each Brand and Category, then update Column "FirstValue" as 1, else 0? e.g of expected table
Date | Brands | Category | Value | FirstValue
Jan 08 | A | 1 | 0 |0
Jan 08 | A | 2 | 0 |0
Jan 08 | A | 3 | 0 |0
Jan 08 | B | 1 | 12 |1
Jan 08 | B | 2 | 0 |0
Jan 08 | B | 3 | 0 |0
Feb 08 | A | 1 | 5 |1
Feb 08 | A | 2 | 0 |0
Feb 08 | A | 3 | 67 |1
Feb 08 | B | 1 | 0 |0
Feb 08 | B | 2 | 0 |0
Feb 08 | B | 3 | 6 |1
回答1:
Common table expressions are actually updatable, and combining CTEs with ranking functions ROW_NUMBER() gives a perfect solution:
with cte as (
select row_number() over (partition by Brand, Category order by Date) as rn
, FirstValue
from Table)
update cte
set FirstValue = case when rn = 1 then 1 else 0 end;
来源：https://stackoverflow.com/questions/3154911/sql-server-update-a-column-if-row-is-the-first-record-in-group