Oracle PL / SQL-根據列的最大值插入值

Question

我正在嘗試將主鍵為PRODUCT的數據（產品，時間戳）從表A，B和C插入表xyz。 所有這三個表都有一個timestamp列以及其他列。 我想插入這三個表（A，B和C）的乘積和時間戳的最大值。

Answer 1

如果表xyz中已經存在產品，則無需指定要發生的事情，因此，在不存在該假設的情況下，可以使用如下查詢：

Insert into XYZ(Product, Timestamp)
Select Product, max(timestamp)
  from (select product, timestamp from a union all
        select product, timestamp from b union all
        select product, timestamp from c)
 group by product

Answer 2

您可以嘗試以下方法：

INSERT INTO xyz
  ( product, timestamp )
SELECT MAX(product) KEEP ( DENSE_RANK FIRST ORDER BY timestamp DESC ) AS product
     , MAX(timestamp)
  FROM a
 UNION ALL
SELECT MAX(product) KEEP ( DENSE_RANK FIRST ORDER BY timestamp DESC ) AS product
     , MAX(timestamp)
  FROM b
 UNION ALL
SELECT MAX(product) KEEP ( DENSE_RANK FIRST ORDER BY timestamp DESC ) AS product
     , MAX(timestamp)
  FROM c;

希望這可以幫助。

Answer 3

根據Sentine的評論更新 ：

試試這個（語法未驗證）：

INSERT INTO xyz (product , timestamp) 
 (
    SELECT product , MAX(A.timestamp) 
      FROM A
    UNION
    SELECT product , MAX(B.timestamp) 
      FROM B
    UNION
    SELECT product , MAX(C.timestamp) 
      FROM C
) ;