[SPARK-28791][DOC] Documentation for Alter table Command
What changes were proposed in this pull request? Document ALTER TABLE statement in SQL Reference Guide. Why are the changes needed? Adding documentation for SQL reference. Does this PR introduce any user-facing change? yes Before: There was no documentation for this. After.       How was this patch tested? Used jekyll build and serve to verify. Closes #25590 from PavithraRamachandran/alter_doc. Authored-by: Pavithra Ramachandran <pavi.rams@gmail.com> Signed-off-by: Sean Owen <sean.owen@databricks.com>
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Pavithra Ramachandran
Sean Owen
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@ -19,4 +19,240 @@ license: |
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limitations under the License.
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---
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**This page is under construction**
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### Description
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`ALTER TABLE` statement changes the schema or properties of a table.
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### RENAME
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`ALTER TABLE RENAME` statement changes the table name of an existing table in the database.
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#### Syntax
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{% highlight sql %}
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ALTER TABLE [db_name.]old_table_name RENAME TO [db_name.]new_table_name
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ALTER TABLE table_name PARTITION partition_spec RENAME TO PARTITION partition_spec;
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{% endhighlight %}
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#### Parameters
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<dl>
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<dt><code><em>old_table_name</em></code></dt>
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<dd>Name of an existing table.</dd>
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</dl>
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<dl>
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<dt><code><em>db_name</em></code></dt>
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<dd>Name of the existing database.</dd>
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</dl>
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<dl>
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<dt><code><em>new_table_name</em></code></dt>
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<dd>New name using which the table has to be renamed.</dd>
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</dl>
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<dl>
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<dt><code><em>partition_spec</em></code></dt>
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<dd>Partition to be renamed.</dd>
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</dl>
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### ADD COLUMNS
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`ALTER TABLE ADD COLUMNS` statement adds mentioned columns to an existing table.
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#### Syntax
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{% highlight sql %}
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ALTER TABLE table_name ADD COLUMNS (col_spec[, col_spec ...])
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{% endhighlight %}
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#### Parameters
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<dl>
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<dt><code><em>table_name</em></code></dt>
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<dd>The name of an existing table.</dd>
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</dl>
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<dl>
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<dt><code><em>COLUMNS (col_spec)</em></code></dt>
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<dd>Specifies the columns to be added to be renamed.</dd>
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</dl>
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### SET AND UNSET
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#### SET TABLE PROPERTIES
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`ALTER TABLE SET` command is used for setting the table properties. If a particular property was already set,
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this overrides the old value with the new one.
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`ALTER TABLE UNSET` is used to drop the table property.
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##### Syntax
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{% highlight sql %}
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--Set Table Properties
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ALTER TABLE table_name SET TBLPROPERTIES (key1=val1, key2=val2, ...)
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--Unset Table Properties
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ALTER TABLE table_name UNSET TBLPROPERTIES [IF EXISTS] (key1, key2, ...)
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{% endhighlight %}
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#### SET SERDE
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`ALTER TABLE SET` command is used for setting the SERDE or SERDE properties in Hive tables. If a particular property was already set,
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this overrides the old value with the new one.
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##### Syntax
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{% highlight sql %}
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--Set SERDE Propeties
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ALTER TABLE table_name [PARTITION part_spec]
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SET SERDEPROPERTIES (key1=val1, key2=val2, ...)
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ALTER TABLE table_name [PARTITION part_spec] SET SERDE serde_class_name
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[WITH SERDEPROPERTIES (key1=val1, key2=val2, ...)]
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{% endhighlight %}
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#### SET LOCATION And SET FILE FORMAT
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`ALTER TABLE SET` command can also be used for changing the file location and file format for
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exsisting tables.
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##### Syntax
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{% highlight sql %}
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--Changing File Format
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ALTER TABLE table_name [PARTITION partition_spec] SET FILEFORMAT file_format;
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--Changing File Location
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ALTER TABLE table_name [PARTITION partition_spec] SET LOCATION 'new_location';
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{% endhighlight %}
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#### Parameters
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<dl>
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<dt><code><em>table_name</em></code></dt>
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<dd>The name of an existing table.</dd>
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</dl>
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<dl>
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<dt><code><em>PARTITION (part_spec)</em></code></dt>
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<dd>Specifies the partition on which the property has to be set.</dd>
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</dl>
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<dl>
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<dt><code><em>SERDEPROPERTIES (key1=val1, key2=val2, ...)</em></code></dt>
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<dd>Specifies the SERDE properties to be set.</dd>
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</dl>
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### Examples
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{% highlight sql %}
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--RENAME table
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DESC student;
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+--------------------------+------------+----------+--+
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| col_name | data_type | comment |
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+--------------------------+------------+----------+--+
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| name | string | NULL |
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| rollno | int | NULL |
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| age | int | NULL |
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| # Partition Information | | |
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| # col_name | data_type | comment |
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| age | int | NULL |
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+--------------------------+------------+----------+--+
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ALTER TABLE Student RENAME TO StudentInfo;
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--After Renaming the table
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DESC StudentInfo;
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+--------------------------+------------+----------+--+
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| col_name | data_type | comment |
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+--------------------------+------------+----------+--+
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| name | string | NULL |
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| rollno | int | NULL |
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| age | int | NULL |
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| # Partition Information | | |
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| # col_name | data_type | comment |
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| age | int | NULL |
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+--------------------------+------------+----------+--+
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--RENAME partition
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SHOW PARTITIONS StudentInfo;
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+------------+--+
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| partition |
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+------------+--+
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| age=10 |
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| age=11 |
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| age=12 |
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+------------+--+
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ALTER TABLE default.StudentInfo PARTITION (age='10') RENAME TO PARTITION (age='15');
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--After renaming Partition
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SHOW PARTITIONS StudentInfo;
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+------------+--+
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| partition |
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+------------+--+
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| age=11 |
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| age=12 |
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| age=15 |
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+------------+--+
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-- Add new column to a table
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DESC StudentInfo;
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+--------------------------+------------+----------+--+
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| col_name | data_type | comment |
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+--------------------------+------------+----------+--+
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| name | string | NULL |
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| rollno | int | NULL |
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| age | int | NULL |
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| # Partition Information | | |
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| # col_name | data_type | comment |
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| age | int | NULL |
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+--------------------------+------------+----------+
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ALTER TABLE StudentInfo ADD columns (LastName string, DOB timestamp);
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--After Adding New columns to the table
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DESC StudentInfo;
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+--------------------------+------------+----------+--+
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| col_name | data_type | comment |
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+--------------------------+------------+----------+--+
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| name | string | NULL |
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| rollno | int | NULL |
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| LastName | string | NULL |
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| DOB | timestamp | NULL |
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| age | int | NULL |
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| # Partition Information | | |
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| # col_name | data_type | comment |
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| age | int | NULL |
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+--------------------------+------------+----------+--+
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--Change the fileformat
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ALTER TABLE loc_orc SET fileformat orc;
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ALTER TABLE p1 partition (month=2, day=2) SET fileformat parquet;
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--Change the file Location
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ALTER TABLE dbx.tab1 PARTITION (a='1', b='2') SET LOCATION '/path/to/part/ways'
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-- SET SERDE/ SERDE Properties
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ALTER TABLE test_tab SET SERDE 'org.apache.hadoop.hive.serde2.columnar.LazyBinaryColumnarSerDe';
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ALTER TABLE dbx.tab1 SET SERDE 'org.apache.madoop' WITH SERDEPROPERTIES ('k' = 'v', 'kay' = 'vee')
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--SET TABLE PROPERTIES
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ALTER TABLE dbx.tab1 SET TBLPROPERTIES ('winner' = 'loser')
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--DROP TABLE PROPERTIES
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ALTER TABLE dbx.tab1 UNSET TBLPROPERTIES ('winner')
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{% endhighlight %}
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### Related Statements
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- [CREATE TABLE](sql-ref-syntax-ddl-create-table.html)
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- [DROP TABLE](sql-ref-syntax-ddl-drop-table.html)
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