甲骨文嵌套相關子問題

Question

考慮Table 1和Table與一對多的關係（表1是主表和表2是詳細表）。我想從table1獲取記錄，其中某些值（'XXX'）是與table1相關的詳細記錄的表2中最近記錄的值。我想這樣做是：

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，由於在相關子查詢的參照表1（T1）是兩個層次深，它與Oracle錯誤（無效ID T1）彈出。我需要能夠重寫這一點，但有一點需要注意的是，只有where子句可能會改變（即最初的select和from必須保持不變）。可以做到嗎？

Answer 1

這裏有一個不同的分析方法行：

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) 

這裏是一個使用排序功能相同的想法：

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

試試這個：

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 3

這是否你在找什麼？

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) 
       ) 

Answer 4

，你可以在這裏使用的分析：加入表1至表2，利用最新表2記錄在表1的每個元素和驗證這最近的元素有「XXX」的值：

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：無需修改頂級SELECT，你可以寫這樣的查詢：

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) 

基本上你只能加入（SEMI-JOIN）從表2是最近每個fk_id