Sql “具有最大日期的行中的属性”的分析函数

我正在重构一位同事的代码，我有几次他使用光标获取与某个谓词匹配的最新行：

他的技巧是将连接作为游标写入，按日期字段降序排列，打开游标，获取第一行，然后关闭游标

这需要为驱动此操作的结果集的每一行调用一个游标，这对于许多行来说代价很高。我更希望能够加入，但还有什么比关联子查询更便宜的呢

select a.id_shared_by_several_rows, a.foo from audit_trail a
where a.entry_date = (select max(a.entry_date) 
                     from audit_trail b 
                     where b.id_shared_by_several_rows = a.id_shared_by_several_rows 
                     );

---

我猜，由于这是一种常见的需求，所以有一个Oracle分析函数可以实现这一点。

有分析等级、密集等级和行编号，用于根据排序标准识别行的序列号。它们在处理顺序列中没有差异的行的方式上有所不同。[例如你可以得到1,1,3或1,1,2或1,2,3。]

select index_name, column_name, column_position,
       rank() over (partition by table_name order by column_position) rnk,
       dense_rank() over (partition by table_name order by column_position) drnk,
       row_number() over (partition by table_name order by column_position) rn
from all_ind_columns
where index_owner = 'SYSMAN'
and table_name = 'MGMT_JOB_EXECUTION';

因为分析是在选定的行上进行的，所以您仍然需要一个子查询/内联视图来过滤掉不需要的行。在本例中，INDEX_NAME是共享标识符

select index_name, column_name
from
  (select index_name, column_name, column_position,
         row_number() over (partition by index_name order by column_position) rn
  from all_ind_columns
  where index_owner = 'SYSMAN'
  and table_name = 'MGMT_JOB_EXECUTION')
where rn = 1;

---

有分析等级、密集等级和行编号，用于根据排序标准识别行的序列号。它们在处理顺序列中没有差异的行的方式上有所不同。[例如你可以得到1,1,3或1,1,2或1,2,3。]

select index_name, column_name, column_position,
       rank() over (partition by table_name order by column_position) rnk,
       dense_rank() over (partition by table_name order by column_position) drnk,
       row_number() over (partition by table_name order by column_position) rn
from all_ind_columns
where index_owner = 'SYSMAN'
and table_name = 'MGMT_JOB_EXECUTION';

因为分析是在选定的行上进行的，所以您仍然需要一个子查询/内联视图来过滤掉不需要的行。在本例中，INDEX_NAME是共享标识符

select index_name, column_name
from
  (select index_name, column_name, column_position,
         row_number() over (partition by index_name order by column_position) rn
  from all_ind_columns
  where index_owner = 'SYSMAN'
  and table_name = 'MGMT_JOB_EXECUTION')
where rn = 1;

---

这将只对数据进行一次传递，并可用于根据需要从表中获取任意多的列，而无需进行自连接

select DISTINCT
       a.id_shared_by_several_rows,
       FIRST_VALUE(a.foo)
       OVER (PARTITION BY a.id_shared_by_several_rows
             ORDER BY a.entry_date DESC)
       AS foo
from audit_trail a;

---

这将只对数据进行一次传递，并可用于根据需要从表中获取任意多的列，而无需进行自连接

select DISTINCT
       a.id_shared_by_several_rows,
       FIRST_VALUE(a.foo)
       OVER (PARTITION BY a.id_shared_by_several_rows
             ORDER BY a.entry_date DESC)
       AS foo
from audit_trail a;

试试这个：

select id_shared_by_several_rows, foo from (
select a.id_shared_by_several_rows, a.foo, a.entry_date, max(a.entry_date) over (partition by a.id_shared_by_several_rows) max_entry_date
from audit_trail_a
) where entry_date = max_entry_date

试试这个：

select id_shared_by_several_rows, foo from (
select a.id_shared_by_several_rows, a.foo, a.entry_date, max(a.entry_date) over (partition by a.id_shared_by_several_rows) max_entry_date
from audit_trail_a
) where entry_date = max_entry_date

---

我相信你想用

select
  max(id_shared_by_several_rows) keep (dense_rank first order by entry_date),
  max(foo                      ) keep (dense_rank first order by entry_date)
from
  audit_trail;

---

我相信你想用

select
  max(id_shared_by_several_rows) keep (dense_rank first order by entry_date),
  max(foo                      ) keep (dense_rank first order by entry_date)
from
  audit_trail;