|Oracle® Database SQL Language Reference
11g Release 1 (11.1)
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Caution:You cannot roll back a
TRUNCATE TABLEstatement, nor can you use a
TABLEstatement to retrieve the contents of a table that has been truncated.
Deallocates all space used by the removed rows except that specified by the
MINEXTENTS storage parameter
NEXT storage parameter to the size of the last extent removed from the segment by the truncation process
Removing rows with the
TRUNCATE TABLE statement can be more efficient than dropping and re-creating a table. Dropping and re-creating a table invalidates dependent objects of the table, requires you to regrant object privileges on the table, and requires you to re-create the indexes, integrity constraints, and triggers on the table and respecify its storage parameters. Truncating has none of these effects.
Removing rows with the
TRUNCATE TABLE statement can be faster than removing all rows with the
DELETE statement, especially if the table has numerous triggers, indexes, and other dependencies.
To truncate a table, the table must be in your schema or you must have
TABLE system privilege.
See Also:"Restrictions on Truncating Tables"
Specify the schema and name of the table to be truncated. This table cannot be part of a cluster. If you omit
schema, then Oracle Database assumes the table is in your own cluster.
You can truncate index-organized tables and temporary tables. When you truncate a temporary table, only the rows created during the current session are removed.
Oracle Database changes the
NEXT storage parameter of
table to be the size of the last extent deleted from the segment in the process of truncation.
Oracle Database also automatically truncates and resets any existing
UNUSABLE indicators for the following indexes on
table: range and hash partitions of local indexes and subpartitions of local indexes.
table is not empty, then the database marks
UNUSABLE all nonpartitioned indexes and all partitions of global partitioned indexes on the table. However, when the table is truncated, the index is also truncated, and a new high water mark is calculated for the index segment. This operation is equivalent to creating a new segment for the index. Therefore, at the end of the truncate operation, the indexes are once again
For a domain index, this statement invokes the appropriate truncate routine to truncate the domain index data.
See Also:Oracle Database Data Cartridge Developer's Guide for more information on domain indexes
If a regular or index-organized table contains LOB columns, then all LOB data and LOB index segments are truncated.
table is partitioned, then all partitions or subpartitions, as well as the LOB data and LOB index segments for each partition or subpartition, are truncated.
Note:When you truncate a table, Oracle Database automatically removes all data in the table's indexes and any materialized view direct-path
INSERTinformation held in association with the table. This information is independent of any materialized view log. If this direct-path
INSERTinformation is removed, then an incremental refresh of the materialized view may lose data.
You cannot individually truncate a table that is part of a cluster. You must either truncate the cluster, delete all rows from the table, or drop and re-create the table.
You cannot truncate the parent table of an enabled foreign key constraint. You must disable the constraint before truncating the table. An exception is that you can truncate the table if the integrity constraint is self-referential.
If a domain index is defined on
table, then neither the index nor any index partitions can be marked
You cannot truncate the parent table of a reference-partitioned table. You must first drop the reference-partitioned child table.
LOG clause lets you specify whether a materialized view log defined on the table is to be preserved or purged when the table is truncated. This clause permits materialized view master tables to be reorganized through export or import without affecting the ability of primary key materialized views defined on the master to be fast refreshed. To support continued fast refresh of primary key materialized views, the materialized view log must record primary key information.
SNAPSHOTis supported in place of
VIEWfor backward compatibility.
See Also:Oracle Database Advanced Replication for more information about materialized view logs and the
STORAGE clauses let you determine what happens to the space freed by the truncated rows. The
STORAGE clause and
STORAGE clause also apply to the space freed by the data deleted from associated indexes.
DROP STORAGE Specify
STORAGE to deallocate all space from the deleted rows from the table except the space allocated by the
MINEXTENTS parameter of the table or cluster. This space can subsequently be used by other objects in the tablespace. Oracle Database also sets the
NEXT storage parameter to the size of the last extent removed from the segment in the truncation process. This is the default.
REUSE STORAGE Specify
STORAGE to retain the space from the deleted rows allocated to the table. Storage values are not reset to the values when the table or cluster was created. This space can subsequently be used only by new data in the table or cluster resulting from insert or update operations. This clause leaves storage parameters at their current settings.
If you have specified more than one free list for the object you are truncating, then the
STORAGE clause also removes any mapping of free lists to instances and resets the high-water mark to the beginning of the first extent.
TRUNCATE TABLE employees_demo;
The preceding statement also removes all data from all indexes on
employees and returns the freed space to the tablespaces containing them.
TRUNCATE TABLE sales_demo PRESERVE MATERIALIZED VIEW LOG; TRUNCATE TABLE orders_demo;