[英]Comparing data from the same column in SQL Server
我有一個表,其中有一個包含如下數據的列:
aaaa;1
aaaa;2
aaaa;3
bbbb;1
cccc;1
dddd;1
dddd;2
我需要在分號( ;
)之后選擇編號最高的數據,如下所示:
aaaa;3
bbbb;1
cccc;1
dddd;2
誰能給我關於如何執行此操作的想法?
就這么簡單:
select
-- Construct the string by left part + max(right part)
LEFT([column], CHARINDEX(';', [column], 0) - 1) + ';' +
MAX(RIGHT([column], LEN([column]) - CHARINDEX(';', [column], 0)))
from
[table]
group by
LEFT([column], CHARINDEX(';', [column], 0) - 1) -- The left part of ';'
使用CharIndex查找分號的位置,然后使用結果進行排序。 下面的示例代碼:
declare @table table (
col1 varchar(25)
)
insert into @table (col1) values ('aaaa;1')
insert into @table (col1) values ('aaaa;2')
insert into @table (col1) values ('aaaa;3')
insert into @table (col1) values ('bbbb;1')
insert into @table (col1) values ('dddd;1')
insert into @table (col1) values ('dddd;2')
select top 1
col1,
charindex(';',col1,0) as SemiColonLocation,
substring(col1, 0, charindex(';',col1,0) + 1) as TextVal,
substring(col1, charindex(';',col1,0) + 1, (len(col1) - charindex(';',col1,0))) as AfterVal
from @table
order by substring(col1, charindex(';',col1,0) + 1, (len(col1) - charindex(';',col1,0))) desc
您可以使用LEFT
, SUBSTRING
和CHARINDEX
函數來實現此目的。 閱讀本文以獲取更多信息。
WITH CteSplit(string, leftString, rightString, RN) AS(
SELECT
string,
LEFT(string, CHARINDEX(';', string, 0) - 1),
CAST(SUBSTRING(string, CHARINDEX(';', string, 0) + 1, LEN(string) - CHARINDEX(';', string, 0)) AS INT),
RN = ROW_NUMBER() OVER(
PARTITION BY
LEFT(string, CHARINDEX(';', string, 0) - 1)
ORDER BY
CAST(SUBSTRING(string, CHARINDEX(';', string, 0) + 1, LEN(string) - CHARINDEX(';', string, 0)) AS INT) DESC
)
FROM TestTable
)
SELECT
string
FROM CteSplit
WHERE RN = 1
您可以像這樣使用rank();
select column_name
from (select a.*,
rank() over(partition by substr(column_name, 1, 4) order by substr(column, 6) desc) as row_num
from table_name a)
where row_num = '1';
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