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Say, I have a big database globalclients which is very very big.

Now, I divide this big database to 100 sub-databases, as:


Each one running in the corresponding country.

Now, I want to do some analysis over all databases. I want to merge them all into the master-database at first: some tables are merged entirely, and some tables are aggregated before merging:

customer_contact:   merged entirely
product_sales:      `select sum(sales), ... group by month` before merging

Do you have any suggestion? What's the english terms related to this technique? "synchronize" or something else?

It will be a great bonus if I can upload only the difference from the sub-database.

I don't know whether I can do it in database-level or not, "synchronize" the distributed databases in Java would be a complex task. is there any support by PostgreSQL-8.4?

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You could use PL/Proxy to set up a frontend, and then write some functions that run the queries that you need. It could be quite tricky, though. You should plan this architecture carefully.

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SQL queries can be run across multiple tables like this:

SELECT SUM(sales) FROM table1, table2 GROUP BY month

You can also use UNION to sequentially retrieve data from multiple queries:

SELECT SUM(sales) FROM table1  GROUP BY month UNION SELECT SUM(sales) FROM table2  GROUP BY month

I don't know about postgresql, but you might be able to create a VIEW table that gives you a way to access all the tables in a merged format to run simpler queries on.

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Maybe I can create a view for tables in remote databases, but create a view for many tables may not work, because the performance is a big issue. – Xiè Jìléi May 3 '11 at 23:05

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