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Faking Oracle statistics for TIMESTAMP columns

Oracle uses object statistics to estimate the amount of data that a query will probably return. This is used to find the best execution plan for the specific case. Having stale statistics is perhaps a major reason for bad execution plans. But sometimes the data changes so frequently that the generation of up to date statistics is not a feasible goal.

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This article outlines my findings of using ROWNUM with the MERGE statement in Oracle.

The pseudo column ROWNUM can be used to limit the result set to a specific number of rows. I have used this often when I had to update a lot of rows but needed to keep the size of the transaction fairly small. Systems using data replication like Materialized Views or Streams get easily out of sync when they have to cope with huge transactions.

The MERGE statement can be used to reconcile two data sets. A new row is inserted if the key is not available in the target table and it gets updated if it already exists.

Have you ever tried to use both at the same time?

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