获取一行SQL

Question

我有下表

Id          Stack
------------------
1             a
1             b
2             c
2             d

我想得到下表的结果。

Id          Stack
------------------
1             a
2             c

我使用DISTINCT，但是它不起作用怎么办？ 使用group by有什么解决方案吗？

Answer 1

CREATE table sampletb(id int, stack varchar(10));

INSERT into sampletb values(1,'a');
INSERT into sampletb values(1,'b');
INSERT into sampletb values(2,'c');
INSERT into sampletb values(2,'d');

SELECT * FROM sampletb;

id          stack
----------- ----------
1           a
1           b
2           c
2           d


SELECT id,
       stack,
       row_number() over (partition by id order by stack) as row_number
from   sampletb;

该查询将为您提供这样的结果。

id          stack      row_number
----------- ---------- --------------------
1           a          1
1           b          2
2           c          1
2           d          2

现在将上述查询作为子查询，并获取具有row_number=1的列，将提供所需的期望输出。

select id,stack from 
       (
       SELECT id,
              stack,
              row_number() over (partition by id order by stack) as row_number 
       FROM   sampletb) x
where  x.row_number=1;

id          stack
----------- ----------
1           a
2           c

Answer 2

select id,stack from (
select id , stack  , row_number() over (partition by id order by stack) as rn
) k where rn=1

Answer 3

我不确定您需要应用确切的逻辑，但这将返回您发布的结果：

SELECT  ID, MIN(Stack) AS Stack
FROM    T
GROUP BY ID

如果您的DBMS允许使用ROW_NUMBER函数，则可以使用更高级的逻辑（问题中未标记）

SELECT  ID, Stack
FROM    (   SELECT  ID,
                    Stack,
                    ROW_NUMBER() OVER(PARTITION BY ID ORDER BY Stack) AS RowNumber
            FROM    T
        ) t
WHERE   RowNumber = 1

Answer 4

这应该有帮助

select Id, min(Stack) from <TABLE_NAME>
group by Id