左连接以获取在其他列中具有值的最新记录

Question

我有 3 张桌子

Table1
-----------
ID   NAME
1    Test1


Table2
-----------
ID   Table1_ID     Table3_ID
1    1             2
2    1             3
3    1             4
Table3
-----------
ID   NAME    DATA
2    Test1   
3    Test2   Data2
4    Test3   

我有来自 Table1 的 ID，需要从 Table3 中获取在 DATA 列中有值的最新记录

这是我的查询，但它不能很好地工作，尤其是处理大量数据时，它真的很慢

SELECT t1.ID FROM Table1 t1
            left JOIN Table2 toa on t1.ID = toa.Table1_ID
            left JOIN Table3 toad on toa.Table3_ID = toad.ID
WHERE toad.ID = (SELECT MAX(toad2.ID)
                 FROM Table3 toad2
                 WHERE toad2.DATA is not null
                   and toad2.ID IN
                       (SELECT toa2.Table3_ID FROM Table2 toa2 WHERE toa2.Table1_ID = t1.ID))

获取这些数据的更有效方法是什么？

Answer 1

您可以简单地使用 WINDOW function 从第三个表中获取最新记录 -

SELECT ID
  FROM (SELECT t1.ID, ROW_NUMBER() OVER(PARTITION BY t1.ID ORDER BY toad.ID DESC) RN
          FROM Table1 t1
          left JOIN Table2 toa ON t1.ID = toa.Table1_ID
          left JOIN Table3 toad ON toa.Table3_ID = toad.ID
                               AND toad.DATA IS NOT NULL
       )
WHERE RN = 1;

Answer 2

如果您使用的是 Oracle 12c 或更高版本，您可以尝试使用OUTER APPLY来获取最新记录。 像这样：

SELECT  t1.id, t1.name, toad.data
FROM    table1 t1
OUTER APPLY ( SELECT  toad.data
              FROM    table2 toa
              INNER JOIN table3 toad ON toad.id = toa.table3_id
              WHERE   toa.table1_id = t1.id
              AND     toad.data is not null
              ORDER BY toad.id DESC
              FETCH FIRST 1 ROW ONLY ) toad

不幸的是，此功能在 11g 中不可用。