如何区分SQL Server上选择多个对象

Question

我们有一个这样的表：

id      date       code
-----------------------
 1      01/10/14   COO1
 2      02/10/14   C002
 3      03/10/14   C004
 1      04/10/14   C001
 2      05/10/14   C002
 3      06/10/14   C004
 3      07/10/14   C005

所需的输出应该是这样的：

id     date       code
-----------------------
1      01/10/14   COO1
2      02/10/14   C002
3      03/10/14   C004
3      07/10/14   C005

我不想选择表格之前是否存在id和代码。

尝试了这个基本的SQL：

SELECT DISTINCT id 
FROM mytable

但这对我无能为力

我该怎么做？

感谢帮助

Answer 1

好像你按照ID和代码进行分组：

SELECT   id, MIN([date]), code
FROM     my_table
GROUP BY id, code

Answer 2

SELECT   id, MIN([date]), code
FROM     my_table
GROUP BY id, code
ORDER BY id, code

Answer 3

我使用了子查询，它为每个代码返回min（date）

  /*CREATE TABLE tbl(
                id   int  ,
                date    varchar(10),
                code varchar(10))
INSERT INTO tbl (id  ,    date   ,    code)
 VALUES
 (1    ,    '01/10/14' ,  'COO1'),
 (2    ,    '02/10/14' ,  'C002'),
 (3    ,    '03/10/14' ,  'C004'), 
 (1    ,    '04/10/14' ,  'C001'),
 (2    ,    '05/10/14' ,  'C002'),
 (3    ,    '06/10/14' ,  'C004'),
 (3    ,    '07/10/14' ,  'C005')*/


SELECT DISTINCT id   ,
              (SELECT t.date
             from (SELECT code, min(date)   date
                  FROM tbl
                  WHERE  code =x.code
                  GROUP by code)  t) date,  
            code
FROM tbl x