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Applies to: 
SQL Server (all supported versions) Azure SQL Database Azure SQL Managed Instance Azure Synapse Analytics Analytics Platform System (PDW)
Removes one or more relational, spatial, filtered, or XML indexes from the current database. You can drop a clustered index and move the resulting table to another filegroup or partition scheme in a single transaction by specifying the MOVE TO option.
The DROP INDEX statement does not apply to indexes created by defining PRIMARY KEY or UNIQUE constraints. To remove the constraint and corresponding index, use ALTER TABLE with the DROP CONSTRAINT clause.
Important
The syntax defined in <drop_backward_compatible_index> will be removed in a future version of Microsoft SQL Server. Avoid using this syntax in new development work, and plan to modify applications that currently use the feature. Use the syntax specified under <drop_relational_or_xml_index> instead. XML indexes cannot be dropped using backward compatible syntax.
Transact-SQL syntax conventions
Syntax
-- Syntax for SQL Server (All options except filegroup and filestream apply to Azure SQL Database.) DROP INDEX [ IF EXISTS ] { <drop_relational_or_xml_or_spatial_index> [ ,...n ] | <drop_backward_compatible_index> [ ,...n ] } <drop_relational_or_xml_or_spatial_index> ::= index_name ON <object> [ WITH ( <drop_clustered_index_option> [ ,...n ] ) ] <drop_backward_compatible_index> ::= [ owner_name. ] table_or_view_name.index_name <object> ::= { database_name.schema_name.table_or_view_name | schema_name.table_or_view_name | table_or_view_name } <drop_clustered_index_option> ::= { MAXDOP = max_degree_of_parallelism | ONLINE = { ON | OFF } | MOVE TO { partition_scheme_name ( column_name ) | filegroup_name | "default" } [ FILESTREAM_ON { partition_scheme_name | filestream_filegroup_name | "default" } ] } -- Syntax for Azure SQL Database DROP INDEX { <drop_relational_or_xml_or_spatial_index> [ ,...n ] } <drop_relational_or_xml_or_spatial_index> ::= index_name ON <object> <object> ::= { database_name.schema_name.table_or_view_name | schema_name.table_or_view_name | table_or_view_name } -- Syntax for Azure Synapse Analytics and Parallel Data Warehouse DROP INDEX index_name ON { database_name.schema_name.table_name | schema_name.table_name | table_name } [;] Note
To view Transact-SQL syntax for SQL Server 2014 and earlier, see Previous versions documentation.
Arguments
IF EXISTS
Applies to: SQL Server ( SQL Server 2016 (13.x) through current version).
Conditionally drops the index only if it already exists.
index_name
Is the name of the index to be dropped.
database_name
Is the name of the database.
schema_name
Is the name of the schema to which the table or view belongs.
table_or_view_name
Is the name of the table or view associated with the index. Spatial indexes are supported only on tables.
To display a report of the indexes on an object, use the sys.indexes catalog view.
Azure SQL Database supports the three-part name format database_name.[schema_name].object_name when the database_name is the current database or the database_name is tempdb and the object_name starts with #.
<drop_clustered_index_option>
Applies to: SQL Server 2008 (10.0.x) and later, SQL Database.
Controls clustered index options. These options cannot be used with other index types.
MAXDOP = max_degree_of_parallelism
Applies to: SQL Server 2008 (10.0.x) and later, SQL Database (Performance Levels P2 and P3 only).
Overrides the max degree of parallelism configuration option for the duration of the index operation. For more information, see Configure the max degree of parallelism Server Configuration Option. Use MAXDOP to limit the number of processors used in a parallel plan execution. The maximum is 64 processors.
Important
MAXDOP is not allowed for spatial indexes or XML indexes.
max_degree_of_parallelism can be:
1
Suppresses parallel plan generation.
>1
Restricts the maximum number of processors used in a parallel index operation to the specified number.
0 (default)
Uses the actual number of processors or fewer based on the current system workload.
For more information, see Configure Parallel Index Operations.
Note
Parallel index operations are not available in every edition of SQL Server. For a list of features that are supported by the editions of SQL Server, see Editions and supported features of SQL Server 2016.
ONLINE = ON | OFF
Applies to: SQL Server 2008 (10.0.x) and later, Azure SQL Database.
Specifies whether underlying tables and associated indexes are available for queries and data modification during the index operation. The default is OFF.
ON
Long-term table locks are not held. This allows queries or updates to the underlying table to continue.
OFF
Table locks are applied and the table is unavailable for the duration of the index operation.
The ONLINE option can only be specified when you drop clustered indexes. For more information, see the Remarks section.
Note
Online index operations are not available in every edition of SQL Server. For a list of features that are supported by the editions of SQL Server, see Editions and supported features of SQL Server 2016.
MOVE TO { partition_scheme_name(column_name) | filegroup_name | "default"
Applies to: SQL Server 2008 (10.0.x) and later. SQL Database supports "default" as the filegroup name.
Specifies a location to move the data rows that currently are in the leaf level of the clustered index. The data is moved to the new location in the form of a heap. You can specify either a partition scheme or filegroup as the new location, but the partition scheme or filegroup must already exist. MOVE TO is not valid for indexed views or nonclustered indexes. If a partition scheme or filegroup is not specified, the resulting table will be located in the same partition scheme or filegroup as was defined for the clustered index.
If a clustered index is dropped by using MOVE TO, any nonclustered indexes on the base table are rebuilt, but they remain in their original filegroups or partition schemes. If the base table is moved to a different filegroup or partition scheme, the nonclustered indexes are not moved to coincide with the new location of the base table (heap). Therefore, even if the nonclustered indexes were previously aligned with the clustered index, they might no longer be aligned with the heap. For more information about partitioned index alignment, see Partitioned Tables and Indexes.
partition_scheme_name ( column_name )
Applies to: SQL Server 2008 (10.0.x) and later, SQL Database.
Specifies a partition scheme as the location for the resulting table. The partition scheme must have already been created by executing either CREATE PARTITION SCHEME or ALTER PARTITION SCHEME. If no location is specified and the table is partitioned, the table is included in the same partition scheme as the existing clustered index.
The column name in the scheme is not restricted to the columns in the index definition. Any column in the base table can be specified.
filegroup_name
Applies to: SQL Server 2008 (10.0.x) and later.
Specifies a filegroup as the location for the resulting table. If no location is specified and the table is not partitioned, the resulting table is included in the same filegroup as the clustered index. The filegroup must already exist.
"default"
Specifies the default location for the resulting table.
Note
In this context, default is not a keyword. It is an identifier for the default filegroup and must be delimited, as in MOVE TO "default" or MOVE TO [default]. If "default" is specified, the QUOTED_IDENTIFIER option must be set ON for the current session. This is the default setting. For more information, see SET QUOTED_IDENTIFIER (Transact-SQL).
FILESTREAM_ON { partition_scheme_name | filestream_filegroup_name | "default" }
Applies to: SQL Server 2008 (10.0.x) and later.
Specifies a location to move the FILESTREAM table that currently is in the leaf level of the clustered index. The data is moved to the new location in the form of a heap. You can specify either a partition scheme or filegroup as the new location, but the partition scheme or filegroup must already exist. FILESTREAM ON is not valid for indexed views or nonclustered indexes. If a partition scheme is not specified, the data will be located in the same partition scheme as was defined for the clustered index.
partition_scheme_name
Specifies a partition scheme for the FILESTREAM data. The partition scheme must have already been created by executing either CREATE PARTITION SCHEME or ALTER PARTITION SCHEME. If no location is specified and the table is partitioned, the table is included in the same partition scheme as the existing clustered index.
If you specify a partition scheme for MOVE TO, you must use the same partition scheme for FILESTREAM ON.
filestream_filegroup_name
Specifies a FILESTREAM filegroup for FILESTREAM data. If no location is specified and the table is not partitioned, the data is included in the default FILESTREAM filegroup.
"default"
Specifies the default location for the FILESTREAM data.
Note
In this context, default is not a keyword. It is an identifier for the default filegroup and must be delimited, as in MOVE TO "default" or MOVE TO [default]. If "default" is specified, the QUOTED_IDENTIFIER option must be ON for the current session. This is the default setting. For more information, see SET QUOTED_IDENTIFIER (Transact-SQL).
Remarks
When a nonclustered index is dropped, the index definition is removed from metadata and the index data pages (the B-tree) are removed from the database files. When a clustered index is dropped, the index definition is removed from metadata and the data rows that were stored in the leaf level of the clustered index are stored in the resulting unordered table, a heap. All the space previously occupied by the index is regained. This space can then be used for any database object.
Note
SQL Server documentation uses the term B-tree generally in reference to indexes. In rowstore indexes, SQL Server implements a B+ tree. This does not apply to columnstore indexes or in-memory data stores. Review SQL Server Index Architecture and Design Guide for details.
An index cannot be dropped if the filegroup in which it is located is offline or set to read-only.
When the clustered index of an indexed view is dropped, all nonclustered indexes and auto-created statistics on the same view are automatically dropped. Manually created statistics are not dropped.
The syntax table_or_view_name.index_name is maintained for backward compatibility. An XML index or spatial index cannot be dropped by using the backward compatible syntax.
When indexes with 128 extents or more are dropped, the Database Engine defers the actual page deallocations, and their associated locks, until after the transaction commits.
Sometimes indexes are dropped and re-created to reorganize or rebuild the index, such as to apply a new fill factor value or to reorganize data after a bulk load. To do this, using ALTER INDEXis more efficient, especially for clustered indexes. ALTER INDEX REBUILD has optimizations to prevent the overhead of rebuilding the nonclustered indexes.
Using Options with DROP INDEX
You can set the following index options when you drop a clustered index: MAXDOP, ONLINE, and MOVE TO.
Use MOVE TO to drop the clustered index and move the resulting table to another filegroup or partition scheme in a single transaction.
When you specify ONLINE = ON, queries and modifications to the underlying data and associated nonclustered indexes are not blocked by the DROP INDEX transaction. Only one clustered index can be dropped online at a time. For a complete description of the ONLINE option, see CREATE INDEX (Transact-SQL).
You cannot drop a clustered index online if the index is disabled on a view, or contains text, ntext, image, varchar(max), nvarchar(max), varbinary(max), or xml columns in the leaf-level data rows.
Using the ONLINE = ON and MOVE TO options requires additional temporary disk space.
After an index is dropped, the resulting heap appears in the sys.indexes catalog view with NULL in the name column. To view the table name, join sys.indexes with sys.tables on object_id. For an example query, see example D.
On multiprocessor computers that are running SQL Server 2005 Enterprise edition or later, DROP INDEX may use more processors to perform the scan and sort operations associated with dropping the clustered index, just like other queries do. You can manually configure the number of processors that are used to run the DROP INDEX statement by specifying the MAXDOP index option. For more information, see Configure Parallel Index Operations.
When a clustered index is dropped, the corresponding heap partitions retain their data compression setting unless the partitioning scheme is modified. If the partitioning scheme is changed, all partitions are rebuilt to an uncompressed state (DATA_COMPRESSION = NONE). To drop a clustered index and change the partitioning scheme requires the following two steps:
Drop the clustered index.
Modify the table by using an ALTER TABLE ... REBUILD ... option specifying the compression option.
When a clustered index is dropped OFFLINE, only the upper levels of clustered indexes are removed; therefore, the operation is quite fast. When a clustered index is dropped ONLINE, SQL Server rebuilds the heap two times, once for step 1 and once for step 2. For more information about data compression, see Data Compression.
XML Indexes
Options cannot be specified when you drop anXML index. Also, you cannot use the table_or_view_name.index_name syntax. When a primary XML index is dropped, all associated secondary XML indexes are automatically dropped. For more information, see XML Indexes (SQL Server).
Spatial Indexes
Spatial indexes are supported only on tables. When you drop a spatial index, you cannot specify any options or use .index_name. The correct syntax is as follows:
DROP INDEX spatial_index_name ON spatial_table_name;
For more information about spatial indexes, see Spatial Indexes Overview.
Permissions
To execute DROP INDEX, at a minimum, ALTER permission on the table or view is required. This permission is granted by default to the sysadmin fixed server role and the db_ddladmin and db_owner fixed database roles.
Examples
A. Dropping an index
The following example deletes the index IX_ProductVendor_VendorID on the ProductVendor table in the AdventureWorks2019 database.
DROP INDEX IX_ProductVendor_BusinessEntityID ON Purchasing.ProductVendor; GO B. Dropping multiple indexes
The following example deletes two indexes in a single transaction in the AdventureWorks2019 database.
DROP INDEX IX_PurchaseOrderHeader_EmployeeID ON Purchasing.PurchaseOrderHeader, IX_Address_StateProvinceID ON Person.Address; GO C. Dropping a clustered index online and setting the MAXDOP option
The following example deletes a clustered index with the ONLINE option set to ON and MAXDOP set to 8. Because the MOVE TO option was not specified, the resulting table is stored in the same filegroup as the index. This examples uses the AdventureWorks2019 database
Applies to: SQL Server 2008 (10.0.x) and later, SQL Database.
DROP INDEX AK_BillOfMaterials_ProductAssemblyID_ComponentID_StartDate ON Production.BillOfMaterials WITH (ONLINE = ON, MAXDOP = 2); GO D. Dropping a clustered index online and moving the table to a new filegroup
The following example deletes a clustered index online and moves the resulting table (heap) to the filegroup NewGroup by using the MOVE TO clause. The sys.indexes, sys.tables, and sys.filegroups catalog views are queried to verify the index and table placement in the filegroups before and after the move. (Beginning with SQL Server 2016 (13.x) you can use the DROP INDEX IF EXISTS syntax.)
Applies to: SQL Server 2008 (10.0.x) and later.
--Create a clustered index on the PRIMARY filegroup if the index does not exist. CREATE UNIQUE CLUSTERED INDEX AK_BillOfMaterials_ProductAssemblyID_ComponentID_StartDate ON Production.BillOfMaterials (ProductAssemblyID, ComponentID, StartDate) ON 'PRIMARY'; GO -- Verify filegroup location of the clustered index. SELECT t.name AS [Table Name], i.name AS [Index Name], i.type_desc, i.data_space_id, f.name AS [Filegroup Name] FROM sys.indexes AS i JOIN sys.filegroups AS f ON i.data_space_id = f.data_space_id JOIN sys.tables as t ON i.object_id = t.object_id AND i.object_id = OBJECT_ID(N'Production.BillOfMaterials','U') GO --Create filegroup NewGroup if it does not exist. IF NOT EXISTS (SELECT name FROM sys.filegroups WHERE name = N'NewGroup') BEGIN ALTER DATABASE AdventureWorks2012 ADD FILEGROUP NewGroup; ALTER DATABASE AdventureWorks2012 ADD FILE (NAME = File1, FILENAME = 'C:\Program Files\Microsoft SQL Server\MSSQL13.MSSQLSERVER\MSSQL\DATA\File1.ndf') TO FILEGROUP NewGroup; END GO --Verify new filegroup SELECT * from sys.filegroups; GO -- Drop the clustered index and move the BillOfMaterials table to -- the Newgroup filegroup. -- Set ONLINE = OFF to execute this example on editions other than Enterprise Edition. DROP INDEX AK_BillOfMaterials_ProductAssemblyID_ComponentID_StartDate ON Production.BillOfMaterials WITH (ONLINE = ON, MOVE TO NewGroup); GO -- Verify filegroup location of the moved table. SELECT t.name AS [Table Name], i.name AS [Index Name], i.type_desc, i.data_space_id, f.name AS [Filegroup Name] FROM sys.indexes AS i JOIN sys.filegroups AS f ON i.data_space_id = f.data_space_id JOIN sys.tables as t ON i.object_id = t.object_id AND i.object_id = OBJECT_ID(N'Production.BillOfMaterials','U'); GO E. Dropping a PRIMARY KEY constraint online
Indexes that are created as the result of creating PRIMARY KEY or UNIQUE constraints cannot be dropped by using DROP INDEX. They are dropped using the ALTER TABLE DROP CONSTRAINT statement. For more information, see ALTER TABLE.
The following example deletes a clustered index with a PRIMARY KEY constraint by dropping the constraint. The ProductCostHistory table has no FOREIGN KEY constraints. If it did, those constraints would have to be removed first.
-- Set ONLINE = OFF to execute this example on editions other than Enterprise Edition. ALTER TABLE Production.TransactionHistoryArchive DROP CONSTRAINT PK_TransactionHistoryArchive_TransactionID WITH (ONLINE = ON); F. Dropping an XML index
The following example drops an XML index on the ProductModel table in the AdventureWorks2019 database.
DROP INDEX PXML_ProductModel_CatalogDescription ON Production.ProductModel; G. Dropping a clustered index on a FILESTREAM table
The following example deletes a clustered index online and moves the resulting table (heap) and FILESTREAM data to the MyPartitionScheme partition scheme by using both the MOVE TO clause and the FILESTREAM ON clause.
Applies to: SQL Server 2008 (10.0.x) and later.
DROP INDEX PK_MyClusteredIndex ON dbo.MyTable WITH (MOVE TO MyPartitionScheme, FILESTREAM_ON MyPartitionScheme); GO See Also
ALTER INDEX (Transact-SQL)
ALTER PARTITION SCHEME (Transact-SQL)
ALTER TABLE (Transact-SQL)
CREATE INDEX (Transact-SQL)
CREATE PARTITION SCHEME (Transact-SQL)
CREATE SPATIAL INDEX (Transact-SQL)
CREATE XML INDEX (Transact-SQL)
EVENTDATA (Transact-SQL)
sys.indexes (Transact-SQL)
sys.tables (Transact-SQL)
sys.filegroups (Transact-SQL)
sp_spaceused (Transact-SQL)
FAQs
Which is the correct query for dropping an index? ›
The DROP INDEX command is used to delete an index in a table.
Should I drop index before inserting? ›Removing indexes prior to large inserts on a table, including when using SQL Bulk Insert, may be a best practice to increase performance.
Do we need to commit after drop index? ›After wasting a lot of time on non-solutions to the problem, I found the real solution is to commit immediately after dropping the index. When commit is issued, the table is unlocked and the insert transactions complete successfully.
Is DELETE faster with index? ›The answer is yes, Indexes do help with the DELETE statement. Let us see a simple example of the SELECT command and its execution plan. Here you will be able to see the query using the index in the execution plan.
How long does dropping an index take? ›An index on a table of the size you mentioned should generally be able to be dropped pretty quickly (and certainly more quickly than 3+ minutes).
What happens when you drop an index? ›If an index is a unique index, it prevents that duplicate values are inserted. If you drop it, unique values could be entered where not appropriate.
When should you avoid indexes? ›- 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.
Having two identical indexes makes a negative impact on the performance of SQL queries. It is actually a waste of disk space and also slows down the insertions to the table. Therefore, it is a good practice to avoid duplicate indexes to eliminate these issues.
When should you avoid indexing? ›- Indexes should not be used on small tables.
- Indexes should not be used on columns that return a high percentage of data rows when used as a filter condition in a query's WHERE clause. ...
- Tables that have frequent, large batch update jobs run can be indexed.
If you update a table, the system has to maintain those indexes that are on the columns being updated. So having a lot of indexes can speed up select statements, but slow down inserts, updates, and deletes.
Can we drop index on primary key? ›
To drop a primary key, the index name is always PRIMARY , which must be specified as a quoted identifier because PRIMARY is a reserved word: DROP INDEX `PRIMARY` ON t; Indexes on variable-width columns of NDB tables are dropped online; that is, without any table copying.
How do I know if my index needs to be rebuilt? ›- If the index has height greater than four, rebuild the index.
- The deleted leaf rows should be less than 20%.
- Removing all the rows fast with truncate.
- Using create-table-as-select to wipe a large fraction of the data.
- Dropping or truncating partitions.
- Using a filtered table move.
Yes, indexes can hurt performance for SELECTs. It is important to understand how database engines operate. Data is stored on disk(s) in "pages". Indexes make it possible to access the specific page that has a specific value in one or more columns in the table.
Why many indexes are not good for performance? ›However, the more indexes you add, the slower your inserts and deletes will go, and the more competition pages will have for precious memory space. You may have to throw hardware at it in the form of more memory and faster storage. Sometimes, even just 5 indexes are too many.
Why does SQL Server drop index take so long? ›The dangers of deleting indexes
Recreating the index might take long : if the table is big (or extremely big) it could take minutes to hours to recreate the index, impacting your application the entire time. Plus, the process of recreating the index adds additional CPU load.
Indexing happens as a background task when nothing else is happening. Alas, the default setting is so discreet that indexing can take days and sometimes never completes. Windows will fully reindex your computer for various reasons including some changes in index/search settings and if the index files become corrupt.
How long does it take to rebuild indexing? ›The rebuild times usually should last less than 10 minutes, but depends on the database size. The index rebuild is atomic operation that is not considered a data corruption threat. When you create or rebuild an index, you can specify a fill factor, which is the amount the data pages in the index that are filled.
Which of the following reasons are included to drop an index? ›Some reasons for dropping an index include: The index is no longer required. The index is not providing anticipated performance improvements for queries issued against the associated table. For example, the table might be very small, or there might be many rows in the table but very few index entries.
Can an index be empty? ›The only restriction is that elements in an Index must be nonnegative. The same value can appear multiple times in an Index. Indexes can be empty.
Can you DELETE an index? ›
To delete an index by using Object Explorer
Expand the table that contains the index you want to delete. Expand the Indexes folder. Right-click the index you want to delete and select Delete.
The downside to adding indexes to a table is that they affect the performance of writes. Moreover, improperly created indexes can even adversely affect SELECT queries! Any table configuration where performance suffers due to excessive, improper, or missing indexes is considered to be poor indexing.
Which columns are not good for indexing? ›A GUID column is not the best candidate for indexing. Indexes are best suited to columns with a data type that can be given some meaningful order, ie sorted (integer, date etc). It does not matter if the data in a column is generally increasing.
Why we shouldn't index every column in the SQL table? ›Indexes take up space in memory (RAM); Too many or too large of indexes and the DB is going to have to be swapping them to and from the disk. They also increase insert and delete time (each index must be updated for every piece of data inserted/deleted/updated). You don't have infinite memory.
How can I increase my indexing speed? ›- Minimize main thread work.
- Reduce JavaScript execution time.
- Ensure text remains visible during webfont load.
A properly created database index can improve query performance by 99% or more.
Which attributes would you generally avoid indexing and why? ›- Indexes should not be used on tables containing few records.
- 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.
- Indexes should not be used on the columns that are frequently manipulated.
The benefits of index investing include low cost, requires little financial knowledge, convenience, and provides diversification. Disadvantages include the lack of downside protection, no choice in index composition, and it cannot beat the market (by definition).
Will disabling indexing improve performance? ›The Windows Search Indexer is only required if you search your directories and files. In other words, if you don't use Windows search to locate specific files or media, you can definitely disable it. In addition, disabling the Windows Search Indexer will result in a noticeable performance improvement.
Does indexing improve update performance? ›Index will improve performance if same column is updating and used in WHERE clause. The big_table is having 5000000 records. This predicate filter WHERE flag_id < 10 filters 8000 records and updating same 8000 records.
How to improve DELETE performance in SQL Server? ›
If you are deleting 95% of a table and keeping 5%, it can actually be quicker to move the rows you want to keep into a new table, drop the old table, and rename the new one. Or copy the keeper rows out, truncate the table, and then copy them back in.
Does indexing reduce table size? ›No, number of columns in a table has no bearing on benefits from having an index. An index is solely on the values in the column(s) specified; it's the frequency of the values that will impact how much benefit your queries will see.
Does indexing take up space? ›Indexing service is creating huge files at below location which is eating up space on hard drive.
How often should you rebuild SQL indexes? ›Categorize fragmentation percentage – Microsoft suggests that we rebuild indexes when we have greater than 30% fragmentation and reorganize when they are in between 5% and 30% fragmentation.
How often should you rebuild indexes? ›Best practices suggest that you should rebuild indexes when fragmentation is greater than 30 percent. When fragmentation is between 10 to 30 percent, reorganizing the index is enough.
Does SQL Server rebuild indexes automatically? ›The SQL Server Database Engine automatically maintains indexes whenever insert, update, or delete operations are made to the underlying data. Over time these modifications can cause the information in the index to become scattered in the database (fragmented).
How to delete 1 million rows in SQL Server? ›By far, the fastest way to delete a bunch of records is to use the TRUNCATE TABLE statement. This is much faster than the DELETE statement because it does not log any of the row-level delete operations. However, you can only use TRUNCATE TABLE : To delete ALL the records in the table.
What is the 80/20 Rule SQL? ›A Pareto chart highlights the most important factors amongst a large number of factors. A social scientist in Italy, Vilfredo Pareto discovered that roughly 20% of the population owned 80% of the wealth.
Is truncate faster than delete? ›While the TRUNCATE command is faster than the DELETE command. To use Delete you need DELETE permission on the table. To use Truncate on a table we need at least ALTER permission on the table. The identity of the fewer column retains the identity after using DELETE Statement on the table.
How to optimize SQL query using index? ›- Understand how database design impacts SQL Server indexes. ...
- Create indexes for your workload requirements. ...
- Create indexes for the most heavily and frequently used queries. ...
- Apply SQL Server index key column best practices. ...
- Analyze the data distribution of your SQL Server index columns.
Is it good to have multiple indexes on a table? ›
Multiple indexes are created on a single table, with each index containing a different set of columns. Multi-column indexes are created on a single table, with each index containing two or more columns. Multiple indexes can improve the performance of queries that use different combinations of columns.
Is it good to create index on multiple columns? ›A multicolumn index should be created when data satisfying multiple conditions is to be retrieved, such as when a complex-condition retrieval using the AND operator with multiple columns as the key is executed.
What happens if you have too many indexes on a table? ›Too many indexes create additional overhead associated with the extra amount of data pages that the Query Optimizer needs to go through. Also, too many indexes require too much space and add to the time it takes to accomplish maintenance tasks.
How many indexes should I create? ›The overall point, however, is how to create the right indexes. To start, I'd say that most tables should have fewer than 15 indexes. In many cases, tables that focus on transaction processing (OLTP) might be in the single digits, whereas tables that are used more for decision support might be well into double digits.
How to drop an index in oracle? ›If you created the index explicitly with the CREATE INDEX statement, then you can drop the index with the DROP INDEX statement. The following statement drops the emp_ename index: DROP INDEX emp_ename; You cannot drop only the index associated with an enabled UNIQUE key or PRIMARY KEY constraint.
How to drop the index in db2? ›Dropping indexes
For dropping the index, you use the following syntax: Syntax: db2 drop unique index <index_name> on <table_name>(<unique_column>) include (<column_names..>)
Starting in MongoDB 5.2, you can use db. collection. dropIndex() to drop existing indexes on the same collection even if there is a build in progress on another index.
How to drop index constraint in oracle? ›- DROP INDEX [schema_name.] ...
- DECLARE index_count INTEGER; BEGIN SELECT COUNT(*) INTO index_count FROM USER_INDEXES WHERE INDEX_NAME = 'index_name'; IF index_count > 0 THEN EXECUTE IMMEDIATE 'DROP INDEX index_name'; END IF; END; / ...
- DROP INDEX members_name_i;
DROP TABLE always removes any indexes, rules, triggers, and constraints that exist for the target table. However, to drop a table that is referenced by a view or a foreign-key constraint of another table, CASCADE must be specified.
Does drop column remove index? ›If columns are dropped from a table, the columns are also removed from any index of which they are a part. If all columns that make up an index are dropped, the index is dropped as well.
How do I drop all indexes in a table in SQL Server? ›
- INSERT INTO #commands (Command) SELECT N'ALTER TABLE ' + QUOTENAME(SCHEMA_NAME(o. schema_id)) ...
- INSERT INTO #commands (Command) SELECT 'DROP INDEX ' + QUOTENAME(i. name) ...
- + '.' + QUOTENAME(OBJECT_NAME(s. object_id)) + '.' ...
- OPEN result_cursor; FETCH NEXT FROM result_cursor INTO @CurrentCommand; WHILE @@FETCH_STATUS = 0.
Expand the table that contains the index you want to delete. Expand the Indexes folder. Right-click the index you want to delete and select Delete. In the Delete Object dialog box, verify that the correct index is in the Object to be deleted grid and click OK.
How do I drop and reset index? ›Import the Pandas module. Create a DataFrame. Drop some rows from the DataFrame using the drop() method. Reset the index of the DataFrame using the reset_index() method.
How do I remove a specific value from an index array? ›Pass the value of the element you wish to remove from your array into the indexOf() method to return the index of the element that matches that value in the array. Then make use of the splice() method to remove the element at the returned index.
How do I drop multiple columns by index? ›Pandas Drop Multiple Columns By Index
You can use df. columns[[index1, index2, indexn]] to identify the list of column names in that index position and pass that list to the drop method. Note that an index is 0 based. Use 0 to delete the first column and 1 to delete the second column and so on.
To delete an index from a collection, use the dropIndex method while specifying the index name to be dropped. Let's remove the user-created index with the index name student name index, as shown below. Result: The dropIndexes command can also drop all the indexes excluding the default _id index.
Can we drop unique index? ›A primary key or unique key index cannot be explicitly dropped. You must use one of the following methods to drop it: If the primary index or unique constraint was created automatically for the primary key or unique key, dropping the primary key or unique key causes the index to be dropped.
What is the difference between index and constraint? ›Index - improves the performance of retrieval and sort operations on Table data. Unique Constraints - a combination of values that uniquely identify a row in the Table.
How do I drop all constraints? ›- To explicitly drop unique constraints, use the DROP UNIQUE clause of the ALTER TABLE statement. ...
- To drop primary key constraints, use the DROP PRIMARY KEY clause of the ALTER TABLE statement. ...
- To drop (table) check constraints, use the DROP CHECK clause of the ALTER TABLE statement.