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An examination of the data access path will assist you in determining whether additional indexes are necessary to improve the performance of the long-running SQL. In particular, look for table scans and large index range scans. In the following example, after evaluating the inner loop of the nested select, it was recommended to add an index on all T2 columns:
The index was created to consist of T2 columns used in the WHERE clause with ROW_ID at the end of the index. This influenced the database optimizer to choose this index for index-only access. Since the query wants the minimum (ROW_ID), the very first qualifying page in the index will also contain the lowest value.
Table S_ORG_EXT has indexes on many columns, but not all columns. If you have a large number of records (several million accounts) in S_ORG_EXT, you may get a performance improvement in deleting and merging by adding an index to one or more of the following:
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