临时表不存储更新的值

Question

I've been trying to create a temp table and update it but when I go to view the temp table, it doesn't show any of the updated rows

declare global temporary table hierarchy (
code varchar(5)
description varchar(30);

INSERT INTO session.hierarchy
SELECT code, 30_description
FROM table1
WHERE code like '_....';

SELECT *
FROM session.hierarchy;

Answer 1

This is a frequently asked question.

When using DGTT with Db2 (declare global temporary table), you need to know that the default is to discard all rows after a COMMIT action. That is the reason the table appears to be empty after you insert - the rows got deleted if autocommit is enabled. If that is not what you want, you should use the on commit preserve rows clause when declaring the table.

It is also very important to the with replace option when creating stored procedures, this is often the most friendly for development and testing, and it is not the default. Otherwise, if the same session attempts to repeat the declaration of the DGTT the second and subsequent attempts will fail because the DGTT already exists.

It can also be interesting for problem determination sometimes to use on rollback preserve rows but that is less often used.

When using a DGTT, one of the main advantages is that you can arrange for the population of the table (inserts, updates ) to be unlogged which can give a great performance boost if you have millions of rows to add to the DGTT.

Suggestion is therefore:

declare global temporary table ... (   )...
not logged
on commit preserve rows
with replace;

For DPF installations, also consider using distribute by hash (...) for best performance.