在SQL Server中对数据进行分组

Question

Please Consider the following table :

As you can see the Name column has some repeated values with is a group like I need to have a query so I can fetch just the first row of a group something like this:

Please take in to account that I need the fastest way because the real table is not like that and could have lots of data to be filter that way.

Thanks in advance.

Answer 1

this depends greatly on how you define 'the first in the group'

something like this:

select name, min(code)
from mytable
group by name
order by name

Answer 2

Assuming the table name is test (change to match yours), try this

CREATE TABLE [dbo].[test](
    [name] [varchar](3) NULL,
    [code] [varchar](5) NULL,
    [RowNumber] [int] NOT NULL,
 CONSTRAINT [PK_test] PRIMARY KEY CLUSTERED 
(
    [RowNumber] ASC
)WITH (PAD_INDEX  = OFF, STATISTICS_NORECOMPUTE  = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS  = ON, ALLOW_PAGE_LOCKS  = ON) ON [PRIMARY]
) ON [PRIMARY]


INSERT INTO [test] ([name],[code],[RowNumber])VALUES('A1','AED',1)
INSERT INTO [test] ([name],[code],[RowNumber])VALUES('A1','BG',2)
INSERT INTO [test] ([name],[code],[RowNumber])VALUES('A1','WS',3)
INSERT INTO [test] ([name],[code],[RowNumber])VALUES('A2','CER',4)
INSERT INTO [test] ([name],[code],[RowNumber])VALUES('A2','HJY',5)
INSERT INTO [test] ([name],[code],[RowNumber])VALUES('A5','OLP',6)
INSERT INTO [test] ([name],[code],[RowNumber])VALUES('A6','LOO',7)
INSERT INTO [test] ([name],[code],[RowNumber])VALUES('A6','AED',8)

SELECT a.*
FROM   dbo.test a
       INNER JOIN(SELECT name,
                         MIN(rownumber) AS rownumber
                  FROM   dbo.test
                  GROUP  BY name) b
         ON a.name = b.name
            AND a.rownumber = b.rownumber
ORDER  BY a.name 

If the RowNumber column is always going to be sequential the put an index on that column.