Редактиране

Споделяне чрез

TRUNCATE TABLE (Transact-SQL)

  • Статия

Applies to: SQL Server Azure SQL Database Azure SQL Managed Instance Azure Synapse Analytics Analytics Platform System (PDW) Warehouse in Microsoft Fabric

Removes all rows from a table or specified partitions of a table, without logging the individual row deletions. TRUNCATE TABLE is similar to the DELETE statement with no WHERE clause; however, TRUNCATE TABLE is faster and uses fewer system and transaction log resources.

Transact-SQL syntax conventions

Syntax

Syntax for SQL Server and Azure SQL Database.

TRUNCATE TABLE
    { database_name.schema_name.table_name | schema_name.table_name | table_name }
    [ WITH ( PARTITIONS ( { <partition_number_expression> | <range> }
    [ , ...n ] ) ) ]
[ ; ]

<range> ::=
<partition_number_expression> TO <partition_number_expression>

Syntax for Microsoft Fabric, Azure Synapse Analytics, and Parallel Data Warehouse.

TRUNCATE TABLE { database_name.schema_name.table_name | schema_name.table_name | table_name }
[ ; ]

Arguments

database_name

The name of the database.

schema_name

The name of the schema to which the table belongs.

table_name

The name of the table to truncate or from which all rows are removed. table_name must be a literal. table_name can't be the OBJECT_ID() function or a variable.

WITH ( PARTITIONS ( { <partition_number_expression> | <range> } [ , ...n ] ) )

Applies to: SQL Server 2016 (13.x) and later versions.

Specifies the partitions to truncate or from which all rows are removed. If the table isn't partitioned, the WITH PARTITIONS argument generates an error. If the WITH PARTITIONS clause isn't provided, the entire table is truncated.

<partition_number_expression> can be specified in the following ways:

  • Provide the number of a partition, for example: WITH (PARTITIONS (2))

  • Provide the partition numbers for several individual partitions separated by commas, for example: WITH (PARTITIONS (1, 5))

  • Provide both ranges and individual partitions, for example: WITH (PARTITIONS (2, 4, 6 TO 8))

  • <range> can be specified as partition numbers separated by the word TO, for example: WITH (PARTITIONS (6 TO 8))

To truncate a partitioned table, the table and indexes must be aligned (partitioned on the same partition function).

Remarks

Compared to the DELETE statement, TRUNCATE TABLE has the following advantages:

  • Less transaction log space is used.

    The DELETE statement removes rows one at a time and records an entry in the transaction log for each deleted row. TRUNCATE TABLE removes the data by deallocating the data pages used to store the table data and records only the page deallocations in the transaction log.

  • Fewer locks are typically used.

    When the DELETE statement is executed using a row lock, each row in the table is locked for deletion. TRUNCATE TABLE always locks the table (including a schema (SCH-M) lock) and page, but not each row.

  • Without exception, zero pages are left in the table.

    After a DELETE statement is executed, the table can still contain empty pages. For example, empty pages in a heap can't be deallocated without at least an exclusive (LCK_M_X) table lock. If the delete operation doesn't use a table lock, the table (heap) will contain many empty pages. For indexes, the delete operation can leave empty pages behind, although a background cleanup process deallocates these pages quickly.

TRUNCATE TABLE removes all rows from a table, but the table structure and its columns, constraints, indexes, and so on, remain. To remove the table definition in addition to its data, use the DROP TABLE statement.

If the table contains an identity column, the counter for that column is reset to the seed value defined for the column. If no seed was defined, the default value 1 is used. To retain the identity counter, use DELETE instead.

A TRUNCATE TABLE operation can be rolled back within a transaction.

Limitations

You can't use TRUNCATE TABLE on tables that:

  • Are referenced by a FOREIGN KEY constraint. You can truncate a table that has a foreign key that references itself.

  • Participate in an indexed view.

  • Are published by using transactional replication or merge replication.

  • Are system-versioned temporal.

  • Are referenced by an EDGE constraint.

For tables with one or more of these characteristics, use the DELETE statement instead.

TRUNCATE TABLE can't activate a trigger because the operation doesn't log individual row deletions. For more information, see CREATE TRIGGER (Transact-SQL).

In Azure Synapse Analytics and Analytics Platform System (PDW):

  • TRUNCATE TABLE isn't allowed within the EXPLAIN statement.

  • TRUNCATE TABLE can't be ran inside of a transaction.

Truncate large tables

Microsoft SQL Server has the ability to drop or truncate tables that have more than 128 extents without holding simultaneous locks on all the extents required for the drop.

Permissions

The minimum permission required is ALTER on table_name. TRUNCATE TABLE permissions default to the table owner, members of the sysadmin fixed server role, and the db_owner and db_ddladmin fixed database roles, and aren't transferable. However, you can incorporate the TRUNCATE TABLE statement within a module, such as a stored procedure, and grant appropriate permissions to the module using the EXECUTE AS clause.

Examples

A. Truncate a table

The following example removes all data from the JobCandidate table. SELECT statements are included before and after the TRUNCATE TABLE statement to compare results.

USE AdventureWorks2022;
GO

SELECT COUNT(*) AS BeforeTruncateCount
FROM HumanResources.JobCandidate;
GO

TRUNCATE TABLE HumanResources.JobCandidate;
GO

SELECT COUNT(*) AS AfterTruncateCount
FROM HumanResources.JobCandidate;
GO

B. Truncate table partitions

Applies to: SQL Server 2016 (13.x) and later versions.

The following example truncates specified partitions of a partitioned table. The WITH (PARTITIONS (2, 4, 6 TO 8)) syntax causes partition numbers 2, 4, 6, 7, and 8 to be truncated.

TRUNCATE TABLE PartitionTable1
WITH (PARTITIONS (2, 4, 6 TO 8));
GO

C. Roll back a truncate operation

The following example demonstrates that a TRUNCATE TABLE operation inside a transaction can be rolled back.

  1. Create a test table with three rows.

    USE [tempdb];
GO
CREATE TABLE TruncateTest (ID INT IDENTITY (1, 1) NOT NULL);
GO
INSERT INTO TruncateTest DEFAULT VALUES;
GO 3

  2. Check the data before truncate.

    SELECT * FROM TruncateTest;
GO

  3. Truncate the table within a transaction, and check the number of rows.

    BEGIN TRANSACTION;

TRUNCATE TABLE TruncateTest;

SELECT * FROM TruncateTest;

    You see that the table is empty.

  4. Roll back the transaction and check the data.

    ROLLBACK TRANSACTION;
GO

SELECT * FROM TruncateTest;
GO

    You see all three rows.

  5. Clean up the table.

    DROP TABLE TruncateTest;
GO

Related content