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When would you use a function based index?
Function-based indexes allow you to create an index based on a function or expression. The value of the function or expression is specified by the person creating the index and is stored in the index. Function-based indexes can involve multiple columns, arithmetic expressions, or maybe a PL/SQL function or C callout.
What do you think should be done to use a function based index?
A function-based index reduces computation for the database. If you have a query that consists of expression and use this query many times, the database has to calculate the expression each time you execute the query. To avoid these computations, you can create a function-based index that has the exact expression.
What is the function index?
The INDEX function returns a value or the reference to a value from within a table or range. There are two ways to use the INDEX function: If you want to return the value of a specified cell or array of cells, see Array form.
Can we create index on nullable column in Oracle?
Hence, Oracle indexes will not include NULL values. To get around the optimization of SQL queries that choose NULL column values, we can create a function-based index using the null value built-in SQL function to index only on the NULL columns.
Is a unique constraint and index?
A unique index ensures that the values in the index key columns are unique. A unique constraint also guarantees that no duplicate values can be inserted into the column(s) on which the constraint is created. When a unique constraint is created a corresponding unique index is automatically created on the column(s).
When do you use a function based index?
Function-Based Indexes. Traditionally, performing a function on an indexed column in the where clause of a query guaranteed an index would not be used.
Which is better concatenated or function based indexes?
Later releases have them enabled by default. This method works for concatenated indexes also. Remember, function-based indexes require more effort to maintain than regular indexes, so having concatenated indexes in this manner may increase the incidence of index maintenance compared to a function-based index on a single column.
What to do when Oracle index is not being used?
In sum, the Oracle optimizer should immediately see a new index and begin using it immediately, invalidating all SQL that might benefit from the index. When Oracle does not use an index, you can force him to use the index with diagnostic tools. Testing to force Oracle to use an index is easy.