Question

考虑table1和table2具有一对多关系（table1是主表，table2是详细信息表）。我想从table1获取记录，其中某些值（'XXX'）是与table1相关的详细记录的table2中最新记录的值。我想做的是：

select t1.pk_id
  from table1 t1
 where 'XXX' = (select a_col
                  from (  select a_col
                            from table2 t2
                           where t2.fk_id = t1.pk_id
                        order by t2.date_col desc)
                 where rownum = 1)

但是，因为相关子查询中对table1（t1）的引用是两级深度的，所以它会弹出一个Oracle错误（无效的id t1）。我需要能够重写这个，但有一点需要注意，只有where子句可以改变（即初始select和from必须保持不变）。可以吗？

Answer 1

这是一种不同的分析方法：

select t1.pk_id
  from table1 t1
 where 'XXX' = (select distinct first_value(t2.a_col)
                                  over (order by t2.date_col desc)
                  from table2 t2
                  where t2.fk_id = t1.pk_id)

以下是使用排名功能的相同想法：

select t1.pk_id
  from table1 t1
 where 'XXX' = (select max(t2.a_col) keep
                          (dense_rank first order by t2.date_col desc)
                  from table2 t2
                  where t2.fk_id = t1.pk_id)

Answer 2

你可以在这里使用分析：将table1连接到table2，获取table1中每个元素的最新table2记录，并验证这个最新元素的值是否为'XXX'：

SELECT *
  FROM (SELECT t1.*, 
               t2.a_col, 
               row_number() over (PARTITION BY t1.pk 
                                  ORDER BY t2.date_col DESC) rnk
           FROM table1 t1
           JOIN table2 t2 ON t2.fk_id = t1.pk_id)
 WHERE rnk = 1
   AND a_col = 'XXX'

更新：无需修改顶级SELECT，您可以编写如下查询：

SELECT t1.pk_id
  FROM table1 t1
 WHERE 'XXX' =
       (SELECT a_col
          FROM (SELECT a_col, 
                       t2_in.fk_id, 
                       row_number() over(PARTITION BY t2_in.fk_id 
                                         ORDER BY t2_in.date_col DESC) rnk
                   FROM table2 t2_in) t2
         WHERE rnk = 1
           AND t2.fk_id = t1.pk_id)

基本上你只加入（SEMI-JOIN）table2中每行最fk_id

的行

Answer 3

试试这个：

select t1.pk_id   
from table1 t1  
where 'XXX' = 
(select a_col 
 from table2 t2                           
 where t2.fk_id = t1.pk_id                         
 and t2.date_col =
   (select max(t3.date_col)
    from table2 t3
    where t3.fk_id = t2.fk_id)
)

Answer 4

这是否符合您的要求？

select t1.pk_id
  from table1 t1
 where 'XXX' = (  select a_col
                    from table2 t2
                   where t2.fk_id = t1.pk_id
                    t2.date_col = (select max(date_col) from table2 where fk_id = t1.pk_id)
                )

Oracle嵌套相关子查询问题

4 个答案: