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   <h1 class="title topictitle1" id="ariaid-title1">TRUNCATE TABLE Statement (<span class="keyword">Impala 2.3</span> or higher only)</h1>


   <div class="body conbody">
     <p class="p">
        Removes
       the data from an Impala table while leaving the table itself. </p>
     <p class="p">
         <strong class="ph b">Syntax:</strong>
       </p>
     <pre class="pre codeblock"><code>TRUNCATE [TABLE] <span class="ph">[IF EXISTS]</span> [<var class="keyword varname">db_name</var>.]<var class="keyword varname">table_name</var></code></pre>
     <p class="p">
         <strong class="ph b">Statement type:</strong> DDL
       </p>
     <p class="p">
         <strong class="ph b">Usage notes:</strong>
       </p>
     <p class="p"> Often used to empty tables that are used during ETL cycles, after the
       data has been copied to another table for the next stage of processing.
       This statement is a low-overhead alternative to dropping and recreating
       the table, or using <code class="ph codeph">INSERT OVERWRITE</code> to replace the data
       during the next ETL cycle. </p>
     <p class="p"> This statement removes all the data and associated data files in the
       table. It can remove data files from internal tables, external tables,
       partitioned tables, and tables mapped to HBase or the Amazon Simple
       Storage Service (S3). The data removal applies to the entire table,
       including all partitions of a partitioned table. </p>
     <p class="p"> Any statistics produced by the <code class="ph codeph">COMPUTE STATS</code> statement
       are reset when the data is removed. </p>
     <p class="p"> Make sure that you are in the correct database before truncating a
       table, either by issuing a <code class="ph codeph">USE</code> statement first or by
       using a fully qualified name
           <code class="ph codeph"><var class="keyword varname">db_name</var>.<var class="keyword varname">table_name</var></code>. </p>
     <p class="p">The optional <code class="ph codeph">TABLE</code> keyword does not affect the behavior
       of the statement.</p>
     <p class="p"> The optional <code class="ph codeph">IF EXISTS</code> clause
       makes the statement succeed whether or not the table exists. If the table
       does exist, it is truncated; if it does not exist, the statement has no
       effect. This capability is useful in standardized setup scripts that are
       might be run both before and after some of the tables exist. This clause
       is available in <span class="keyword">Impala 2.5</span> and higher. </p>
     <p class="p">
         For other tips about managing and reclaiming Impala disk space, see
         <a class="xref" href="../shared/../topics/impala_disk_space.html#disk_space">Managing Disk Space for Impala Data</a>.
       </p>
     <p class="p">
         <strong class="ph b">Amazon S3 considerations:</strong>
       </p>
     <p class="p"> Although Impala cannot write new data to a table stored in
       the Amazon S3 filesystem, the <code class="ph codeph">TRUNCATE TABLE</code> statement
       can remove data files from S3. See <a class="xref" href="impala_s3.html#s3">Using Impala with Amazon S3 Object Store</a> for
       details about working with S3 tables. </p>
     <p class="p">
         <strong class="ph b">Cancellation:</strong> Cannot be cancelled.
       </p>
     <p class="p">
         <strong class="ph b">HDFS permissions:</strong>
       </p>
     <p class="p"> The user ID that the <span class="keyword cmdname">impalad</span> daemon runs
       under, typically the <code class="ph codeph">impala</code> user, must have write
       permission for all the files and directories that make up the table. </p>
     <p class="p">
         <strong class="ph b">Kudu considerations:</strong>
       </p>
     <p class="p">
         Currently, the <code class="ph codeph">TRUNCATE TABLE</code> statement cannot be used with Kudu
         tables.
       </p>
     <p class="p">
         <strong class="ph b">Examples:</strong>
       </p>
     <p class="p"> The following example shows a table containing some data and with table
       and column statistics. After the <code class="ph codeph">TRUNCATE TABLE</code>
       statement, the data is removed and the statistics are reset. </p>
     <pre class="pre codeblock"><code>CREATE TABLE truncate_demo (x INT);
 INSERT INTO truncate_demo VALUES (1), (2), (4), (8);
 SELECT COUNT(*) FROM truncate_demo;
 +----------+
 | count(*) |
 +----------+
 | 4        |
 +----------+
 COMPUTE STATS truncate_demo;
 +-----------------------------------------+
 | summary                                 |
 +-----------------------------------------+
 | Updated 1 partition(s) and 1 column(s). |
 +-----------------------------------------+
 SHOW TABLE STATS truncate_demo;
 +-------+--------+------+--------------+-------------------+--------+-------------------+
 | #Rows | #Files | Size | Bytes Cached | Cache Replication | Format | Incremental stats |
 +-------+--------+------+--------------+-------------------+--------+-------------------+
 | 4     | 1      | 8B   | NOT CACHED   | NOT CACHED        | TEXT   | false             |
 +-------+--------+------+--------------+-------------------+--------+-------------------+
 SHOW COLUMN STATS truncate_demo;
 +--------+------+------------------+--------+----------+----------+
 | Column | Type | #Distinct Values | #Nulls | Max Size | Avg Size |
 +--------+------+------------------+--------+----------+----------+
 | x      | INT  | 4                | -1     | 4        | 4        |
 +--------+------+------------------+--------+----------+----------+

 -- After this statement, the data and the table/column stats will be gone.
 TRUNCATE TABLE truncate_demo;

 SELECT COUNT(*) FROM truncate_demo;
 +----------+
 | count(*) |
 +----------+
 | 0        |
 +----------+
 SHOW TABLE STATS truncate_demo;
 +-------+--------+------+--------------+-------------------+--------+-------------------+
 | #Rows | #Files | Size | Bytes Cached | Cache Replication | Format | Incremental stats |
 +-------+--------+------+--------------+-------------------+--------+-------------------+
 | -1    | 0      | 0B   | NOT CACHED   | NOT CACHED        | TEXT   | false             |
 +-------+--------+------+--------------+-------------------+--------+-------------------+
 SHOW COLUMN STATS truncate_demo;
 +--------+------+------------------+--------+----------+----------+
 | Column | Type | #Distinct Values | #Nulls | Max Size | Avg Size |
 +--------+------+------------------+--------+----------+----------+
 | x      | INT  | -1               | -1     | 4        | 4        |
 +--------+------+------------------+--------+----------+----------+
 </code></pre>
     <p class="p"> The following example shows how the <code class="ph codeph">IF EXISTS</code> clause
       allows the <code class="ph codeph">TRUNCATE TABLE</code> statement to be run without
       error whether or not the table exists: </p>
     <pre class="pre codeblock"><code>CREATE TABLE staging_table1 (x INT, s STRING);
 Fetched 0 row(s) in 0.33s

 SHOW TABLES LIKE 'staging*';
 +----------------+
 | name           |
 +----------------+
 | staging_table1 |
 +----------------+
 Fetched 1 row(s) in 0.25s

 -- Our ETL process involves removing all data from several staging tables
 -- even though some might be already dropped, or not created yet.

 TRUNCATE TABLE IF EXISTS staging_table1;
 Fetched 0 row(s) in 5.04s

 TRUNCATE TABLE IF EXISTS staging_table2;
 Fetched 0 row(s) in 0.25s

 TRUNCATE TABLE IF EXISTS staging_table3;
 Fetched 0 row(s) in 0.25s
 </code></pre>
     <p class="p">
         <strong class="ph b">Related information:</strong>
       </p>
     <p class="p">
       <a class="xref" href="impala_tables.html#tables">Overview of Impala Tables</a>, <a class="xref" href="impala_alter_table.html#alter_table">ALTER TABLE Statement</a>, <a class="xref" href="impala_create_table.html#create_table">CREATE TABLE Statement</a>, <a class="xref" href="impala_partitioning.html#partitioning">Partitioning for Impala Tables</a>, <a class="xref" href="impala_tables.html#internal_tables">Internal Tables</a>, <a class="xref" href="impala_tables.html#external_tables">External Tables</a>
     </p>
   </div>
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	<h1 class="title topictitle1" id="ariaid-title1">TRUNCATE TABLE Statement (<span class="keyword">Impala 2.3</span> or higher only)</h1>



	<div class="body conbody">
	<p class="p">
	Removes
	the data from an Impala table while leaving the table itself. </p>
	<p class="p">
	<strong class="ph b">Syntax:</strong>
	</p>
	<pre class="pre codeblock"><code>TRUNCATE [TABLE] <span class="ph">[IF EXISTS]</span> [<var class="keyword varname">db_name</var>.]<var class="keyword varname">table_name</var></code></pre>
	<p class="p">
	<strong class="ph b">Statement type:</strong> DDL
	</p>
	<p class="p">
	<strong class="ph b">Usage notes:</strong>
	</p>
	<p class="p"> Often used to empty tables that are used during ETL cycles, after the
	data has been copied to another table for the next stage of processing.
	This statement is a low-overhead alternative to dropping and recreating
	the table, or using <code class="ph codeph">INSERT OVERWRITE</code> to replace the data
	during the next ETL cycle. </p>
	<p class="p"> This statement removes all the data and associated data files in the
	table. It can remove data files from internal tables, external tables,
	partitioned tables, and tables mapped to HBase or the Amazon Simple
	Storage Service (S3). The data removal applies to the entire table,
	including all partitions of a partitioned table. </p>
	<p class="p"> Any statistics produced by the <code class="ph codeph">COMPUTE STATS</code> statement
	are reset when the data is removed. </p>
	<p class="p"> Make sure that you are in the correct database before truncating a
	table, either by issuing a <code class="ph codeph">USE</code> statement first or by
	using a fully qualified name
	<code class="ph codeph"><var class="keyword varname">db_name</var>.<var class="keyword varname">table_name</var></code>. </p>
	<p class="p">The optional <code class="ph codeph">TABLE</code> keyword does not affect the behavior
	of the statement.</p>
	<p class="p"> The optional <code class="ph codeph">IF EXISTS</code> clause
	makes the statement succeed whether or not the table exists. If the table
	does exist, it is truncated; if it does not exist, the statement has no
	effect. This capability is useful in standardized setup scripts that are
	might be run both before and after some of the tables exist. This clause
	is available in <span class="keyword">Impala 2.5</span> and higher. </p>
	<p class="p">
	For other tips about managing and reclaiming Impala disk space, see
	<a class="xref" href="../shared/../topics/impala_disk_space.html#disk_space">Managing Disk Space for Impala Data</a>.
	</p>
	<p class="p">
	<strong class="ph b">Amazon S3 considerations:</strong>
	</p>
	<p class="p"> Although Impala cannot write new data to a table stored in
	the Amazon S3 filesystem, the <code class="ph codeph">TRUNCATE TABLE</code> statement
	can remove data files from S3. See <a class="xref" href="impala_s3.html#s3">Using Impala with Amazon S3 Object Store</a> for
	details about working with S3 tables. </p>
	<p class="p">
	<strong class="ph b">Cancellation:</strong> Cannot be cancelled.
	</p>
	<p class="p">
	<strong class="ph b">HDFS permissions:</strong>
	</p>
	<p class="p"> The user ID that the <span class="keyword cmdname">impalad</span> daemon runs
	under, typically the <code class="ph codeph">impala</code> user, must have write
	permission for all the files and directories that make up the table. </p>
	<p class="p">
	<strong class="ph b">Kudu considerations:</strong>
	</p>
	<p class="p">
	Currently, the <code class="ph codeph">TRUNCATE TABLE</code> statement cannot be used with Kudu
	tables.
	</p>
	<p class="p">
	<strong class="ph b">Examples:</strong>
	</p>
	<p class="p"> The following example shows a table containing some data and with table
	and column statistics. After the <code class="ph codeph">TRUNCATE TABLE</code>
	statement, the data is removed and the statistics are reset. </p>
	<pre class="pre codeblock"><code>CREATE TABLE truncate_demo (x INT);
	INSERT INTO truncate_demo VALUES (1), (2), (4), (8);
	SELECT COUNT(*) FROM truncate_demo;
	+----------+
	\| count(*) \|
	+----------+
	\| 4 \|
	+----------+
	COMPUTE STATS truncate_demo;
	+-----------------------------------------+
	\| summary \|
	+-----------------------------------------+
	\| Updated 1 partition(s) and 1 column(s). \|
	+-----------------------------------------+
	SHOW TABLE STATS truncate_demo;
	+-------+--------+------+--------------+-------------------+--------+-------------------+
	\| #Rows \| #Files \| Size \| Bytes Cached \| Cache Replication \| Format \| Incremental stats \|
	+-------+--------+------+--------------+-------------------+--------+-------------------+
	\| 4 \| 1 \| 8B \| NOT CACHED \| NOT CACHED \| TEXT \| false \|
	+-------+--------+------+--------------+-------------------+--------+-------------------+
	SHOW COLUMN STATS truncate_demo;
	+--------+------+------------------+--------+----------+----------+
	\| Column \| Type \| #Distinct Values \| #Nulls \| Max Size \| Avg Size \|
	+--------+------+------------------+--------+----------+----------+
	\| x \| INT \| 4 \| -1 \| 4 \| 4 \|
	+--------+------+------------------+--------+----------+----------+

	-- After this statement, the data and the table/column stats will be gone.
	TRUNCATE TABLE truncate_demo;

	SELECT COUNT(*) FROM truncate_demo;
	+----------+
	\| count(*) \|
	+----------+
	\| 0 \|
	+----------+
	SHOW TABLE STATS truncate_demo;
	+-------+--------+------+--------------+-------------------+--------+-------------------+
	\| #Rows \| #Files \| Size \| Bytes Cached \| Cache Replication \| Format \| Incremental stats \|
	+-------+--------+------+--------------+-------------------+--------+-------------------+
	\| -1 \| 0 \| 0B \| NOT CACHED \| NOT CACHED \| TEXT \| false \|
	+-------+--------+------+--------------+-------------------+--------+-------------------+
	SHOW COLUMN STATS truncate_demo;
	+--------+------+------------------+--------+----------+----------+
	\| Column \| Type \| #Distinct Values \| #Nulls \| Max Size \| Avg Size \|
	+--------+------+------------------+--------+----------+----------+
	\| x \| INT \| -1 \| -1 \| 4 \| 4 \|
	+--------+------+------------------+--------+----------+----------+
	</code></pre>
	<p class="p"> The following example shows how the <code class="ph codeph">IF EXISTS</code> clause
	allows the <code class="ph codeph">TRUNCATE TABLE</code> statement to be run without
	error whether or not the table exists: </p>
	<pre class="pre codeblock"><code>CREATE TABLE staging_table1 (x INT, s STRING);
	Fetched 0 row(s) in 0.33s

	SHOW TABLES LIKE 'staging*';
	+----------------+
	\| name \|
	+----------------+
	\| staging_table1 \|
	+----------------+
	Fetched 1 row(s) in 0.25s

	-- Our ETL process involves removing all data from several staging tables
	-- even though some might be already dropped, or not created yet.

	TRUNCATE TABLE IF EXISTS staging_table1;
	Fetched 0 row(s) in 5.04s

	TRUNCATE TABLE IF EXISTS staging_table2;
	Fetched 0 row(s) in 0.25s

	TRUNCATE TABLE IF EXISTS staging_table3;
	Fetched 0 row(s) in 0.25s
	</code></pre>
	<p class="p">
	<strong class="ph b">Related information:</strong>
	</p>
	<p class="p">
	<a class="xref" href="impala_tables.html#tables">Overview of Impala Tables</a>, <a class="xref" href="impala_alter_table.html#alter_table">ALTER TABLE Statement</a>, <a class="xref" href="impala_create_table.html#create_table">CREATE TABLE Statement</a>, <a class="xref" href="impala_partitioning.html#partitioning">Partitioning for Impala Tables</a>, <a class="xref" href="impala_tables.html#internal_tables">Internal Tables</a>, <a class="xref" href="impala_tables.html#external_tables">External Tables</a>
	</p>
	</div>
	<nav role="navigation" class="related-links"><div class="familylinks"><div class="parentlink"><strong>Parent topic:</strong> <a class="link" href="../topics/impala_langref_sql.html">Impala SQL Statements</a></div></div></nav></article></main></body></html>