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POJet Database and pass-through queries, parameters
 

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  1. POJet Database and pass-through queries, parameters
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    <p>I'm connecting to a Jet 4 DB through ODBC. The Jet DB uses pass-through queries to an Oracle DB. This works so far (can't access the p-t queries directly, but creating a view on the query does the trick).</p> <p>I need some subset of the data returned by the p-ts. Parameters would be best, but are not supported.</p> <p>Two questions:</p> <p>1) Jet does seem to be able to push some where-clauses to Oracle. Eg I have a passthrough query that returns 100k rows. A view on the p-t with a single flitering clause (eg "district = '1010'") is very fast, so the processing seems to happen on Oracle. Adding more clauses can slow the query down to a crawl, looping for minutes with high CPU utilization. Is there any documentation on what is passed on and what is done on in the Jet side?</p> <p>2) There are lots of tutorials on how to create dynamic passthrough queries with VBA/Access. Is it possible to do this (or anything to that effect) with Jet accessed through ODBC?</p> <p>Thanks Martin</p> <p><strong>Edit:</strong> Sorry for being so unclear. </p> <p>I have a reporting tool that accesses a Jet db through ODBC. The Jet db contains some data and several passthrough queries to an Oracle db. A typical use case would be a generating report for a given department and a given date, using data from Jet and Oracle. This works very well in principle.</p> <p>The problem is that passthrough queries cannot contain any parameters. A passthrough query works like a view, so I can simply execute "select * from pt_query where dep = 'a' and date = somedate". Jet, however, loads all rows from the pt and does a full scan on the client side. This is unusably slow for a 100k-rows view and I need to find a way to avoid that. </p> <p>For <em>some</em> simple selects, Jet does seem to let Oracle do the hard work and does not load all rows, hence my question 1.</p> <p>If that doesn't work, I need to find a way to force Jet to load only the data I need from Oracle for a given request. </p> <p>I know that I can modify pts through Access VBA, but I only connect through ODBC, so I can only pass SQL to Jet, not call the vb api (unless its possible to inline VB in the SQL statement). </p>
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    1. COWhy is Jet necessary if you are querying Oracle? Why not use ODBC & ADO http://www.connectionstrings.com/oracle ?
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    2. COAs always, business policy... I can't create tables or upload arbitray data on the Oracle data warehouse. I'm joining some custom data currently stored in Access/Jet with data from the Oracle db.
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    3. COWhat Jet passes off to a server database is going to depend on the server database involved and how well the ODBC driver is written. Jet will request as much metadata as it can to optimize the query and send as much of it as possible to the server for processing. I'd look at your SQL trace to see what's causing the slowdown with more criteria. I will note that when I look at the traces in SQL Server, simple queries from Jet with criteria are executed with a generic parameterized sproc. I would expect something similar in Oracle.
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