What is an index and types of indexes. How many number of
indexes can be used per table ?
Answers were Sorted based on User's Feedback
Answer / guest
Index is a method used for faster retrieval of
records.different types of indexes are
1.primary key index
5.function based index
6.B-tree index(default index created) on table.
7.Virtual index(which do not show entry in DBA_segment).
|Is This Answer Correct ?||127 Yes||35 No|
Answer / swapna vamsi
Indexs are used for the faster retrivel of data.
two types of indexes
Cluster index,unclustered index
we can have one cluster index and uotp 249 cluster indexes
for a table
|Is This Answer Correct ?||63 Yes||38 No|
Answer / diptabhaskar ray
the ordering of a table in a database is called index.it
helps in fast access to the specific information.the column
suitable for index should be a primary key or a foreign
key,should be sorted,joins should be allowed and users will
search for data.clustered index and non clustered index.
|Is This Answer Correct ?||20 Yes||17 No|
Answer / jeevan
Index is nothing but an identification of each row. It will be used for quick search.
Types Of Index:
Clustered index is a physical sorting of database table’s rows in a storage media. For this reason, each table may have one clustered index. If a primary key constraint is created for a table but no clustered index exists for a table, then SQL server automatically create a clustered index on a primary key.
Non Clustered Index:
Non clustered index are created outside of the table and contain a sorted list of references to a table itself. Maximum we can use 249 clustered indexes per table.
Only 1 clustered Index can be used per table.
Maximum 249 non clustered index can be used per table.
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Answer / swapna vamsi
upto 249 unclustered indexes per table
|Is This Answer Correct ?||30 Yes||28 No|
Answer / madhu
Index Type Usage
B-tree Default, balanced tree index; good for high-cardinality (high degree of distinct
values) columns. Use a normal B-tree index unless you have a concrete reason
to use a different index type or feature.
Index organized table: Efficient when most of the column values are included in the primary key. You
access the index as if it were a table. The data is stored in a B-tree like
Unique : A form of B-tree index; used to enforce uniqueness in column values. Often
used with primary key and unique key constraints, but can be created
independently of constraints.
Reverse-key : A form of B-tree index; useful to balance I/O in an index that has many
Key-compressed : Good for concatenated indexes where the leading column is often repeated;
compresses leaf block entries. This feature applies to a B-tree or an IOT index.
Descending A form of B-tree index; used with indexes where corresponding column values
are sorted in a descending order (the default order is ascending). You can’t
specify descending for a reverse key index and Oracle ignores descending if
the index type is bitmap.
Bitmap: Excellent in data warehouse environments with low-cardinality columns and
SQL statements using many AND or OR operators in the WHERE clause. Bitmap
indexes aren’t appropriate for online transaction processing (OLTP) databases
where rows are frequently updated. You can’t create a unique bitmap index.
Bitmap join : Useful in data warehouse environments for queries that utilize Star schema
structures that join fact and dimension tables.
Function-based : Good for columns that have SQL functions applied to them. This can be used
with either a B-tree or bitmap index.
Indexed virtual column : An index defined on a virtual column (of a table); useful for columns that have
SQL functions applied to them; viable alternative to using a function-based
Virtual Allows you to create an index with no physical segment or extents via the
NOSEGMENT clause of CREATE INDEX; useful in tuning SQL without consuming
resources required to build the physical index. Any index type can be created
Invisible : The index is not visible to the query optimizer. However, the structure of the
index is maintained as table data is modified. Useful for testing an index
before making it visible to the application. Any index type can be created as
Global partitioned Global index : across all partitions in a partitioned table or regular table. This
can be a B-tree index type and can’t be a bitmap index type.
Local partitioned Local index based on individual partitions in a partitioned table. This can be
either a B-tree or bitmap index type.
Domain Specific for an application or cartridge.
B-tree cluster Used with clustered tables.
Hash cluster Used with hash cluste
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Answer / alekhya
index is a database object used for increasing the
types of indexes:
composite unique index
key compression index
function based index
Reverse key index
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Answer / gunja
there are five types of index they are:
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Answer / deepa
A table can have any number of indexes. However, the more indexes there are, the more overhead is incurred as the table is modified. Specifically, when rows are inserted or deleted, all indexes on the table must be updated as well. Also, when a column is updated, all indexes that contain the column must be updated.
|Is This Answer Correct ?||8 Yes||11 No|
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