Oracle PL / SQL-根据列的最大值插入值

Question

我正在尝试将主键为PRODUCT的数据（产品，时间戳）从表A，B和C插入表xyz。 所有这三个表都有一个timestamp列以及其他列。 我想插入这三个表（A，B和C）的乘积和时间戳的最大值。

Answer 1

如果表xyz中已经存在产品，则无需指定要发生的事情，因此，在不存在该假设的情况下，可以使用如下查询：

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

您可以尝试以下方法：

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;

希望这可以帮助。

Answer 3

根据Sentine的评论更新 ：

试试这个（语法未验证）：

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
) ;