Oracle PL / SQL-根据列的最大值插入值

Question

I am trying to insert data (product, timestamp) into a table xyz from tables A, B & C with a primary key as PRODUCT. All the three table have a timestamp column along with other columns. I want to insert row with product and max of timestamp of these three tables (A, B & C).

Answer 1

You don't specify what you want to happen if product already exists in table xyz, so on the assumption that it doesn't, you could use a query like this:

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

You might try the following:

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;

Hope this helps.

Answer 3

UPDATED as per Sentine's comment:

Try this (syntax not verified):

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
) ;