Multi-database queries

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Multi-database queries

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Overview

A query (typed in SQL code) can operate on different databases: HFSQL, Oracle, SQL Server, ...

You can perform a join between a query on a database of one type and a query on a database of another type.

Therefore, the data can be found in different databases. You have the ability to extract and aggregate data from any source.

This feature is very useful for managing existing Information Systems.

Remark: From version 19, HFSQL is the new name of HyperFileSQL.

How to proceed?

To better understand the operating mode of the multi-database queries, let's look at a simple example:

On an Oracle database, the following query (named MyQry1) is run by HExecuteSQLQuery. This query is used to select the record numbers of the customers.

SELECT Customer.CUUniqueKey+10 AS CUUniqueKey10 FROM Customer
On a HFSQL database, the following query (named MyQry2) is run by HExecuteSQLQuery. This query is used to select the record numbers of the customers and their order number.

SELECT CUUNIQUEKEY,Orders.OrderNumber AS ORDERNUM FROM ORDERS
The multi-database query executed is as follows:

SELECT * FROM MyQry1,MyQry2
WHERE MyQry2.CUUniqueKey=MyQry1.CUUniqueKey10
AND (MyQry2.ORDERNUM = '37348' OR MyQry1.CUUniqueKey10=80)

This query is run itself by HExecuteSQLQuery.