Oracle holds undo information in case you need to roll back a transaction and also to keep a read-consistent version of data. Learn why this can sometimes cause Snapshot Too Old errors.
Read More
When distributed queries can’t be avoided, use IN clauses, set operators such as UNION and MINUS, and use everything else you can to reduce the network traffic between database nodes. Learn more.
Read More
This article exanmies three excellent uses for bitmap join indexes in Oracle: on columns other than the join; on multiple columns; and on multiple tables.
Read More
In a three-table join, Oracle joins two of the tables and joins the result with the third table. Learn how Oracle determines which is the driving table in a query.
Read More
Unlike Oracle fast full scans that have a single index satisfying the entire query, INDEX-MERGE joins have multiple indexes satisfying the entire query. Learn how this impacts performance.
Read More
HASH joins in Oracle can be effective when the lack of a useful index renders NESTED LOOPS joins inefficient. Learn more.
Read More
If two row sources being joined are actually tables that are part of a cluster, and if the join is an equijoin between the cluster keys of the two tables, then Oracle can use a CLUSTER join. Learn more.
Read More
In a SORT-MERGE join, Oracle sorts the first row source by its join columns, sorts the second row source by its join columns, and then merges the sorted row sources together. Learn more.
Read More
NESTED LOOPS joins in Oracle are ideal when the driving row source is small and the joined columns of the inner row source are uniquely indexed or have a highly selective nonunique index. Learn more.
Read More
There are five primary join methods in Oracle, each with a unique set of features and limitations. Answer these 5 questions before you attack a potential join issue.
Read More
Learn about some signiticant changes to the Oracle 11g optimzer that can affect SQL query tuning.
Read More
It’s generally best to use the EXISTS function in Oracle instead of the IN function. Learn more.
Read More