Question

当前SQL：

select t1.*
  from table t1
 where t1.id in ('2', '3', '4')

目前的结果：

id | seq
---+----
 3 |   5
 2 |   7
 2 |   5
 3 |   7
 4 |   3

尝试选择最大值：

select t1.*
  from table t1
 where t1.id in ('2', '3', '4')
   and t1.seq = (select max(t2.seq)
                   from table2 t2
                  where t2.id = t1.id)

由于我使用in列表，这显然不起作用。如何调整我的SQL以获得这些预期结果：

id | seq
---+----
 2 |   7
 3 |   7
 4 |   3

Answer 1

Group By是你的朋友：

SELECT 
    id,
    MAX(seq) seq
FROM TABLE
GROUP BY id

编辑：对评论的回应。要从匹配max seq和id的表中获取其余数据，只需加入表：

SELECT t1.*
FROM TABLE t1
INNER JOIN (
    SELECT 
        id
        MAX(seq) as seq
    FROM TABLE
    GROUP BY id
) as t2
on t1.id = t2.id
and t1.seq = t2.seq

编辑：Gordon和Jean-Francois是正确的你也可以使用ROW_NUMBER（）分析函数来获得相同的结果。您需要检查应用程序的性能差异（我没有检查）。这是一个例子：

SELECT *
FROM (
    SELECT ROW_NUMBER() OVER (
        PARTITION BY id 
        ORDER BY seq DESC) as row_num
        ,*
    FROM TABLE
) as TMP
WHERE row_num = 1

Answer 2

此SQL查询将为您提供来自个人ID的最大序列号。

SELECT t1.*
FROM t1
WHERE t1.id in ('2', '3', '4')
   AND NOT EXISTS (
                    SELECT * 
                    FROM t1 t2
                    WHERE t2.id = t1.id 
                    AND t2.seq > t1.seq

Answer 3

select *
from table
where (id,seq) in
(
select id,max(seq)
from table
group by id
having id in ('2','3','4')
);

即如果id和/或seq完全属于该表的PK。

Answer 4

这是另一个例子，使用我在前面评论中提到的第一个/最后一个方法：

with sd as (select 3 id, 5 seq, 1 dummy from dual union all
            select 2 id, 7 seq, 2 dummy from dual union all
            select 2 id, 5 seq, 3 dummy from dual union all
            select 3 id, 7 seq, 4 dummy from dual union all
            select 3 id, 7 seq, 5 dummy from dual union all
            select 4 id, 3 seq, 6 dummy from dual)
select id,
       max(seq) max_seq,
       max(dummy) keep (dense_rank first order by seq desc) max_rows_dummy
from   sd
group by id;

        ID    MAX_SEQ MAX_ROWS_DUMMY
---------- ---------- --------------
         2          7              2
         3          7              5
         4          3              6

keep (dense_rank first order by ...)位请求在行的顺序列表中保持与等级1相关联的值。如果多于一行的等级为1，则max(...)位存在;它只是打破关系的一种方式。

按组最多行数

4 个答案: