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and other objects you may not be familiar with such as CDB_OBJECTS_AE: Welcome to 12c.
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WHERE table_name = 'T2';
-- repeat the query without a hint
WHERE person_id = 221;
-- note that Oracle uses the index and the cost is much lower
Another Index Quality Query
SELECT dt.table_name, di.index_name, blocks, clustering_factor, (blocks/clustering_factor) CF_RATIO
FROM dba_tables dt, dba_indexes di
WHERE dt.owner NOT LIKE '%SYS%'
AND dt.owner = di.owner
AND dt.table_name = di.table_name
AND dt.blocks > 0
AND di.clustering_factor > (blocks*5)
ORDER BY 5;