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What to do if SQL refuses to use the index?
If this simple SQL refuses to use the index, then there is a fundamental problem. Get the DBA to drop and rebuild the index. If the sample SQL above doesuse the index, then start with your original SQL and remove lines one at a time, running each successively smaller SQL through Explain Planas you go.
What does it mean when an index is not being used?
It means the index tree is being used to go directly to the records we need. Index Scan: Not so good as an index seek, so it could be better. However, sometimes even an index scan is good, a non clustered index scan means the pages of that index are smaller an better for a scan than the pages of the clustered index.
Why is the index not used in the where clause?
If the INDEXhint did not work (ie. Oracle is still using Full Table Scan, Full Index Scan, or a different index), then there is something about the SQL preventing the index from being used. How are indexed column(s) used in the WHERE clause?
How can I tell if my table is not indexed?
It will tell you if your table isn’t indexed ideally for the query you want to run. It depends! These will not rely on the index, because the index is not useful. Click on “display estimated execution plan” to confirm potential index usage. in Oracle databases this is called a Composite Index ( 12g docs but valid for earlier versions)
Do you need to specify index in SQL?
No, no Need to specify explicitly. DB engine should automatically select the index to use based on query execution plans it builds from @Tudor Constantin answer.
When is the index not being used in XML?
However, analysing the query plan XML you will discover the index is most being used for updates, meaning the index is being updated when a record is updated. The plans where the index is being used for update are not needed for us on this query, they are exactly what create problems for performance.
When to use an index in a SELECT statement?
Depending on your RDBMS you can force the use of an index, although it is not recommended unless you know what you are doing. In general you should index columns that you use in table join’s and where statements By using the column that the index is applied to within your conditions, it will be included automatically.
Why is the index not being used in Oracle?
Run your SQL through Explain Planand confirmed that the desired index is not being used. Checked the statisticson the underlying table. Confirmed that the index exists. Oracle will ignore an index for a number of reasons, but they boil down to two possibilities:
What to do if the index is being ignored?
Get the DBA to drop and rebuild the index. If the sample SQL above doesuse the index, then start with your original SQL and remove lines one at a time, running each successively smaller SQL through Explain Planas you go. Somewhere between the original SQL and the one above, the index will start to work.