New truncate table feature (DROP ALL STORAGE) in Oracle 11gR2 11.2.0.2 New truncate table feature (DROP ALL STORAGE) in Oracle 11gR2 11.2.0.2 Starting with Oracle 11gR2 11.2.0.2 there is a new clause added to the truncate table SQL statement allowing to release the space allocated even for extents corresponding to the minextents storage clause. Re: TRUNCATE multaple Tables??? 430321 Oct 17, 2007 7:02 AM ( in response to 591131 ) No, there is no way to truncate multiple tables in one go.

Summary: in this tutorial, you will learn how to use the Oracle TRUNCATE TABLE statement to delete all data from a table faster and more efficiently.

The TRUNCATE TABLE statement is a DDL command, so it includes an implicit COMMIT, so there is no way to issue a ROLLBACK if you decide you didn't want to remove the rows. In the following example, we check the number of rows in the table, issue the TRUNCATE TABLE statement, immediately ROLLBACK and check the number of rows in the table again. TRUNCATE transactions can be rolled back in database engines like SQL Server and PostgreSQL, but not in MySQL and Oracle. TRUNCATE is faster than DELETE, as it doesn't scan every record before removing it. TRUNCATE TABLE locks the whole table to remove data from a table; thus, this command also uses less transaction space than DELETE. Oracle TRUNC (date) function: The TRUNC (date) function returns the date with the time portion of the day truncated to a specific unit of measure. This tutorial explains how to use the TRUNC (date) function with syntax, parameters, examples and explanation.

Introduction to Oracle `TRUNCATE TABLE` statement

When you want to delete all data from a table, you use the DELETE statement without theWHERE clause as follows:

For a table with a small number of rows, the DELETE statement does a good job. However, when you have a table with a large number of rows, using the DELETE statement to remove all data is not efficient.

Oracle introduced the TRUNCATE TABLE statement that allows you to delete all rows from a big table.

The following illustrates the syntax of the Oracle TRUNCATE TABLE statement:

By default, to remove all rows from a table, you specify the name of the table that you want to truncate in the TRUNCATE TABLE clause:

In this case, because we don’t specify the schema name explicitly, Oracle assumes that we truncate the table from our own schema.

If a table has relationships with other tables via the foreign key constraints, you need to use the CASCADE clause:

In this case, the TRUNCATE TABLE CASCADE statement deletes all rows from the table_name, and recursively truncates down the associated tables in the chain.

Note that the TRUNCATE TABLE CASCADE statement requires the foreign key constraints defined with the ON DELETE CASCADE clause to work.

The MATERIALIZED VIEW LOG clause allows you to specify whether a materialized view log defined on the table is to be preserved or purged when the table is truncated. By default, the material view log is preserved.

The STORAGE clause allows you to choose either drop or reuse storage freed by the truncated rows and associated indexes if any. By default, the storage is dropped.

Note that to truncate a table, it must be in your own schema or you must have the DROP ANY TABLE system privilege.

Oracle `TRUNCATE TABLE` examples

Let’s look at some examples of using the TRUNCATE TABLE statement.

A) Oracle `TRUNCATE TABLE` simple example

The following statement creates a table named customers_copy and copies data from the customers table in the sample database:

To delete all rows from the customers_copy table you use the following TRUNCATE TABLE statement:

B) Oracle `TRUNCATE TABLE CASCADE` example

First, let’s createquotations and quotation_items tables for the demonstration:

Next, insert some rows into these two tables:

Then, truncate the quotation table:

The statement failed and Oracle returned the following error:

To fix this, you add the CASCADE clause to the TRUNCATE TABLE statement above:

This statement deleted data from not only quotations table but also quotation_items table.

Finally, verify whether the data from both quotations and quotation_items are deleted or not:

Notice that if we did not specify the ON DELETE CASCADE for the fk_quotation constraint, the TRUNCATE TABLE CASCADE statement above would fail.

In this tutorial, you have learned how to use Oracle TRUNCATE TABLE statement to delete all data from a table faster and more efficiently.

In SQL, the TRUNCATE TABLE statement is a Data Definition Language (DDL) operation that marks the extents of a table for deallocation (empty for reuse). The result of this operation quickly removes all data from a table, typically bypassing a number of integrity enforcing mechanisms. It was officially introduced in the SQL:2008 standard.

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.

The TRUNCATE TABLE mytable statement is logically (though not physically) equivalent to the DELETE FROM mytable statement (without a WHERE clause). The following characteristics distinguish TRUNCATE TABLE from DELETE:

In the Oracle Database, TRUNCATE is implicitly preceded and followed by a commit operation. (This may also be the case in MySQL, when using a transactional storage engine.)
Typically, TRUNCATE TABLE quickly deletes all records in a table by deallocating the data pages used by the table. This reduces the resource overhead of logging the deletions, as well as the number of locks acquired. Records removed this way cannot be restored in a rollback operation. Two notable exceptions to this rule are the implementations found in PostgreSQL and Microsoft SQL Server, both of which allow TRUNCATE TABLE statements to be committed or rolled back transactionally.
You cannot specify a WHERE clause in a TRUNCATE TABLE statement—it is all or nothing.
TRUNCATE TABLE cannot be used when a foreign key references the table to be truncated, since TRUNCATE TABLE statements do not fire triggers. This could result in inconsistent data because ON DELETE/ON UPDATE triggers would not fire.
In some computer systems, TRUNCATE TABLE resets the count of an Identity column back to the identity's seed.
In Microsoft SQL Server 2000 and beyond in full recovery mode, every change to the database is logged, so TRUNCATE TABLE statements can be used for tables involved in log shipping.^[1]
IBM Db2 supports TRUNCATE TABLE in 9.7 or later.

References[edit]

^'Description of the effects of nonlogged and minimally logged operations on transaction log backup and the restore process in SQL Server'. Microsoft. December 2005.

Oracle Truncate Command

Oracle Truncate Table Privilege

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Introduction to Oracle TRUNCATE TABLE statement

Oracle TRUNCATE TABLE examples

A) Oracle TRUNCATE TABLE simple example