[英]How can I create this conditional grouped field on SQL Server 2008?
Sorry for this question, but i cannot resolve this simple query. 抱歉这个问题,但我无法解决这个简单的查询。
I have this table: 我有这张桌子:
ID_Type Item
-----------------
A 1
P 2
P 3
A 4
P 5
A 6
I need to calculate a "group" incremental counter based on ID_Type Field where This field has an "A" Value. 我需要根据ID_Type字段计算“组”增量计数器,其中该字段具有“ A”值。 This is the expected result:
这是预期的结果:
ID_Type Item Counter
-----------------------------
A 1 1
P 2 1
P 3 1
A 4 2
P 5 2
A 6 3
So every time a record with ID_Type='A' appear, I need to increment the counter. 因此,每次出现ID_Type ='A'的记录时,我都需要增加计数器。 Any help will be apreciated.
任何帮助将不胜感激。
In SQL Server 2012+, you can use a cumulative sum: 在SQL Server 2012+中,您可以使用累积总和:
select t.*,
sum(case when id_type = 'A' then 1 else 0 end) over (order by item) as counter
from t;
This will be much more efficient than a correlated subquery approach, particularly on larger data sets. 这将比相关子查询方法更有效,尤其是在较大的数据集上。
One way is a subquery: 一种方法是子查询:
SELECT ID_Type, Item, (
SELECT COUNT(*) FROM MyTable t2
WHERE t2.Item <= t1.Item
AND t2.ID_Type='A'
) AS Counter
FROM MyTable t1
ORDER BY Item ASC
This will work on any version of SQL Server. 这将适用于任何版本的SQL Server。
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