Indexes in Sql server

Vamsi k

7y995

Hi Everyone,

Can anyone of you please post the detailed explanation of Indexes in SQL. ?

What is Indexes?

Types of Indexes?

Reasons why do we use indexes?

Advantages and Dis-advantages?

Regards,

Vamsi

8 Replies

Know the answer? Post it — somebody with the same question will find it here.

Salman Beg5y ago
You can see this link also, https://docs.microsoft.com/en-us/sql/relational-databases/indexes/clustered-and-nonclustered-indexes-described?view=sql-server-ver15 https://www.c-sharpcorner.com/UploadFile/8af593/index-in-sql-server/
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Varun Setia5y ago
Hi, it is very vast topic. There are very good explanations shared by people above. I would also recommend you to have a look at official documentation, dig deeper in docs for more details, https://docs.microsoft.com/en-us/sql/relational-databases/indexes/indexes?view=sql-server-ver15
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Ravinder Sharma5y ago
Syntax to create clustered index:
CREATE CLUSTERED INDEX index_Name
on Schema_Name.table_name (Columns)

Syntax to create Non-clustered index :
CREATE [NONCLUSTERED] INDEX index_Name
on Schema_Name.table_name (Columns)

How to check indexes for the mentioned table?
EXEC SP_HELPINDEX 'schema_name.table_name';
How to rename the indexes?
EXEC SP_RENAME 'OldIndexName', 'NewIndexName', 'INDEX';
How to drop indexes?
DROP INDEX removes one or more indexes from current database.
DROP INDEX [IF EXISTS] INDEX_NAME ON TABLE_NAME
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Mageshwaran R6y ago

Hi,

--Indexes

Indexes are special lookup tables that the database search engine can use to speed up data retrieval.

Simply put, an index is a pointer to data in a table.

Types:

Clustered(Implicit Indexes)

Nonclustered(Explicit Indexes)

Index should be reconsidered.

Indexes should not be used on small tables.

Tables that have frequent, large batch updates or insert operations.

Indexes should not be used on columns that contain a high number of NULL values.

Columns that are frequently manipulated should not be indexed.

Query:

select * From EMPLOYEE where , ---first primary column declare second index column

CREATE INDEX idx_Employee ON EMPLOYEE (JOINDATE);

CREATE UNIQUE INDEX idx_Employee1 on EMPLOYEE (JOINDATE);

CREATE INDEX idx_Employee2 on EMPLOYEE (EMP_NAME, JOINDATE);

DROP INDEX idx_Employee on EMPLOYEE ;

select *from idx employee

Siddhartha Sharma7y ago

Indexes are two types in sql server cluster and non- cluster. Cluster index might be 0 or 1. In the table, cluster index can’t be more than one. While we can put any number of non- cluster indexes. Generally we use the indexes to improve search results.

Tamal Marick7y ago

What is Indexes?

Indexes are used to retrieve data from the database very fast. The users cannot see the indexes, they are just used to speed up searches/queries.

Note: Updating a table with indexes takes more time than updating a table without (because the indexes also need an update). So, only create indexes on columns that will be frequently searched against.

There are two types of Indexes in SQL Server:

Clustered Index

Non-Clustered Index

Clustered Index

A clustered index defines the order in which data is physically stored in a table. Table data can be sorted in only way, therefore, there can be only one clustered index per table. In SQL Server, the primary key constraint automatically creates a clustered index on that particular column.

Non-Clustered Indexes

A non-clustered index doesn’t sort the physical data inside the table. In fact, a non-clustered index is stored at one place and table data is stored in another place. This is similar to a textbook where the book content is located in one place and the index is located in another. This allows for more than one non-clustered index per table.

It is important to mention here that inside the table the data will be sorted by a clustered index. However, inside the non-clustered index data is stored in the specified order. The index contains column values on which the index is created and the address of the record that the column value belongs to.

When a query is issued against a column on which the index is created, the database will first go to the index and look for the address of the corresponding row in the table. It will then go to that row address and fetch other column values. It is due to this additional step that non-clustered indexes are slower than clustered indexes.

Advantages and Disadvantages of Indexes in SQL Server

https://dotnettutorials.net/lesson/advantages-and-disadvantages-of-indexes-sql-server/

Sivakumar Koneti7y ago

Hello read once you can get an idea

https://www.c-sharpcorner.com/UploadFile/8af593/index-in-sql-server/

Jignesh Kumar7y ago

Hi Vamsi,

Please find below links for SQL index where you can understand how exactly index works in SQL,

http://www.sqlservertutorial.net/sql-server-indexes/sql-server-create-index/

https://www.mssqltips.com/sqlservertip/1206/understanding-sql-server-indexing/